diff --git a/frontend/app/api/payments/intents/[intentId]/submit/route.ts b/frontend/app/api/payments/intents/[intentId]/submit/route.ts
index f44956f0..1f988734 100644
--- a/frontend/app/api/payments/intents/[intentId]/submit/route.ts
+++ b/frontend/app/api/payments/intents/[intentId]/submit/route.ts
@@ -37,8 +37,14 @@ export async function POST(
     );
     if (!res.ok) {
       const raw = await res.text();
+      let detail = raw.slice(0, 350);
+      try {
+        const parsed = JSON.parse(raw);
+        if (parsed.detail) detail = String(parsed.detail).slice(0, 350);
+      } catch {}
       const response = buildUpstreamErrorResponse(res.status, raw, {
         detailLimit: 350,
+        error: detail || undefined,
       });
       return applyAuthResponseCookies(response, auth.response);
     }
diff --git a/frontend/app/api/payments/intents/[intentId]/validate/route.ts b/frontend/app/api/payments/intents/[intentId]/validate/route.ts
new file mode 100644
index 00000000..7142c129
--- /dev/null
+++ b/frontend/app/api/payments/intents/[intentId]/validate/route.ts
@@ -0,0 +1,59 @@
+import { NextRequest, NextResponse } from "next/server";
+import {
+  applyAuthResponseCookies,
+  buildBackendRequestHeaders,
+} from "@/lib/backend-auth";
+import {
+  buildProxyExceptionResponse,
+  buildUpstreamErrorResponse,
+} from "@/lib/api-proxy";
+
+const API_BASE = process.env.POLYWEATHER_API_BASE_URL;
+
+export async function POST(
+  req: NextRequest,
+  context: { params: Promise<{ intentId: string }> },
+) {
+  if (!API_BASE) {
+    return NextResponse.json(
+      { error: "POLYWEATHER_API_BASE_URL is not configured" },
+      { status: 500 },
+    );
+  }
+  const { intentId } = await context.params;
+  try {
+    const body = await req.json();
+    const auth = await buildBackendRequestHeaders(req);
+    const proxiedHeaders = new Headers(auth.headers);
+    proxiedHeaders.set("Content-Type", "application/json");
+    const res = await fetch(
+      `${API_BASE}/api/payments/intents/${encodeURIComponent(intentId)}/validate`,
+      {
+        method: "POST",
+        headers: proxiedHeaders,
+        body: JSON.stringify(body ?? {}),
+        cache: "no-store",
+      },
+    );
+    if (!res.ok) {
+      const raw = await res.text();
+      let detail = raw.slice(0, 350);
+      try {
+        const parsed = JSON.parse(raw);
+        if (parsed.detail) detail = String(parsed.detail).slice(0, 350);
+      } catch {}
+      const response = buildUpstreamErrorResponse(res.status, raw, {
+        detailLimit: 350,
+        error: detail || undefined,
+      });
+      return applyAuthResponseCookies(response, auth.response);
+    }
+    const data = await res.json();
+    const response = NextResponse.json(data);
+    return applyAuthResponseCookies(response, auth.response);
+  } catch (error) {
+    return buildProxyExceptionResponse(error, {
+      publicMessage: "Failed to validate payment tx",
+    });
+  }
+}
diff --git a/frontend/components/account/AccountCenter.tsx b/frontend/components/account/AccountCenter.tsx
index 670983ce..36e4269b 100644
--- a/frontend/components/account/AccountCenter.tsx
+++ b/frontend/components/account/AccountCenter.tsx
@@ -945,6 +945,14 @@ export function AccountCenter() {
     CreatedIntent["direct_payment"] | null
   >(null);
   const [manualTxHash, setManualTxHash] = useState("");
+  const [txValidation, setTxValidation] = useState<{
+    loading: boolean;
+    checked: boolean;
+    valid?: boolean;
+    reason?: string;
+    detail?: string;
+    checks?: Record<string, unknown>;
+  }>({ loading: false, checked: false });
   const [paymentMethodTab, setPaymentMethodTab] = useState<"wallet" | "manual">("wallet");
   const [lastPaymentStartedAt, setLastPaymentStartedAt] = useState(0);
   const [showSecondarySections, setShowSecondarySections] = useState(false);
@@ -1520,6 +1528,67 @@ export function AccountCenter() {
     reconcileBusy,
   ]);
 
+  const handleSubmit409 = useCallback(
+    async (intentId: string, txHashNorm: string, raw: string) => {
+      const lowerRaw = raw.toLowerCase();
+      // If intent was already confirmed (maybe by confirm loop), reconcile
+      if (
+        lowerRaw.includes("已支付") ||
+        lowerRaw.includes("already confirmed") ||
+        lowerRaw.includes("already paid")
+      ) {
+        const ok = await reconcileLatestPayment();
+        if (ok) return;
+        setPaymentInfo("该订单已支付，正在恢复订阅...");
+        await loadSnapshot();
+        await loadPaymentSnapshot();
+        return;
+      }
+      // If intent expired, tell user to create a new order
+      if (lowerRaw.includes("expired")) {
+        throw new Error("支付订单已过期（30分钟有效），请重新创建订单。");
+      }
+      // Try fetching intent status as fallback
+      try {
+        const headers = await buildAuthedHeaders(true, false);
+        const intentRes = await fetch(`/api/payments/intents/${intentId}`, {
+          headers,
+          cache: "no-store",
+        });
+        if (intentRes.ok) {
+          const intentJson = (await intentRes.json()) as {
+            intent?: { status?: string; tx_hash?: string };
+          };
+          const status = intentJson.intent?.status;
+          if (status === "confirmed") {
+            await reconcileLatestPayment();
+            const txHash =
+              intentJson.intent?.tx_hash || txHashNorm;
+            setPaymentInfo(
+              `支付已确认，交易: ${shortAddress(txHash)}`,
+            );
+            setPaymentError("");
+            await loadSnapshot();
+            await loadPaymentSnapshot();
+            return;
+          }
+          if (status === "expired") {
+            throw new Error("支付订单已过期（30分钟有效），请重新创建订单。");
+          }
+        }
+      } catch (e) {
+        if (e instanceof Error && e.message !== raw) throw e;
+      }
+      throw new Error(`submit tx failed: ${raw}`);
+    },
+    [
+      buildAuthedHeaders,
+      loadPaymentSnapshot,
+      loadSnapshot,
+      reconcileLatestPayment,
+    ],
+  );
+
   useEffect(() => {
     if (!authIsAuthenticated) return;
     if (backend?.subscription_active) return;
@@ -2535,6 +2604,10 @@ export function AccountCenter() {
       );
       if (!submitRes.ok) {
         const raw = (await submitRes.text()).slice(0, 350);
+        if (submitRes.status === 409) {
+          await handleSubmit409(intentId, txHashNorm, raw);
+          return;
+        }
         throw new Error(`submit tx failed: ${raw}`);
       }
 
@@ -2707,6 +2780,10 @@ export function AccountCenter() {
       );
       if (!submitRes.ok) {
         const raw = (await submitRes.text()).slice(0, 350);
+        if (submitRes.status === 409) {
+          await handleSubmit409(intentId, txHashNorm, raw);
+          return;
+        }
         throw new Error(`submit tx failed: ${raw}`);
       }
       const confirmRes = await fetch(
@@ -2738,6 +2815,7 @@ export function AccountCenter() {
       setPaymentInfo(`支付确认成功，交易: ${shortAddress(txHashNorm)}`);
       setManualPayment(null);
       setManualTxHash("");
+      setTxValidation({ loading: false, checked: false });
       trackAppEvent("checkout_succeeded", {
         entry: "account_center_manual_transfer",
         plan_code: selectedPlan?.plan_code || "pro_monthly",
@@ -2753,6 +2831,42 @@ export function AccountCenter() {
     }
   };
 
+  const validateTxHash = useCallback(
+    async (intentId: string, hash: string) => {
+      const hashNorm = String(hash || "").trim().toLowerCase();
+      if (!hashNorm.startsWith("0x") || hashNorm.length !== 66) {
+        setTxValidation({ loading: false, checked: false });
+        return;
+      }
+      setTxValidation({ loading: true, checked: false });
+      try {
+        const headers = await buildAuthedHeaders(true, false);
+        const res = await fetch(`/api/payments/intents/${intentId}/validate`, {
+          method: "POST",
+          headers,
+          body: JSON.stringify({ tx_hash: hashNorm }),
+        });
+        const json = (await res.json()) as {
+          valid?: boolean;
+          reason?: string;
+          detail?: string;
+          checks?: Record<string, unknown>;
+        };
+        setTxValidation({
+          loading: false,
+          checked: true,
+          valid: Boolean(json.valid),
+          reason: json.reason,
+          detail: json.detail,
+          checks: json.checks,
+        });
+      } catch {
+        setTxValidation({ loading: false, checked: false });
+      }
+    },
+    [buildAuthedHeaders],
+  );
+
   const handleOverlayCheckout = async () => {
     if (!paymentHostAllowed) {
       setPaymentError(
@@ -3512,17 +3626,53 @@ export function AccountCenter() {
                               </p>
                               <input
                                 value={manualTxHash}
-                                onChange={(event) =>
-                                  setManualTxHash(event.target.value)
-                                }
+                                onChange={(event) => {
+                                  setManualTxHash(event.target.value);
+                                  void validateTxHash(
+                                    manualPayment.intent_id ||
+                                      lastIntentId ||
+                                      "",
+                                    event.target.value,
+                                  );
+                                }}
                                 placeholder="0x..."
                                 className="mt-1 w-full rounded-xl border border-white/10 bg-black/30 px-3 py-2 font-mono text-xs text-slate-100 outline-none focus:border-emerald-400/50"
                               />
+                              {txValidation.loading ? (
+                                <p className="mt-1 text-[10px] text-slate-500">
+                                  验证中...
+                                </p>
+                              ) : txValidation.checked && txValidation.valid ? (
+                                <p className="mt-1 text-[10px] text-emerald-400">
+                                  收款地址和金额匹配
+                                </p>
+                              ) : txValidation.checked &&
+                                txValidation.valid === false ? (
+                                <p className="mt-1 text-[10px] text-red-400">
+                                  {txValidation.reason ===
+                                  "tx_not_mined"
+                                    ? "交易未上链，请等待"
+                                    : txValidation.reason === "receiver_mismatch"
+                                      ? "收款地址不匹配！请检查是否转到了正确的地址"
+                                      : txValidation.reason ===
+                                          "amount_insufficient"
+                                        ? "转账金额不足"
+                                        : txValidation.reason === "tx_reverted"
+                                          ? "该交易已回滚"
+                                          : txValidation.detail ||
+                                            "验证失败: " +
+                                              (txValidation.reason ||
+                                                "未知错误")}
+                                </p>
+                              ) : null}
                             </div>
                             <button
                               type="button"
                               onClick={() => void submitManualPaymentTx()}
-                              disabled={paymentBusy}
+                              disabled={
+                                paymentBusy ||
+                                (txValidation.checked && !txValidation.valid)
+                              }
                               className="w-full rounded-xl bg-emerald-600 px-3 py-2 text-xs font-bold text-white transition-all hover:bg-emerald-500 disabled:opacity-50"
                             >
                               {copy.paymentManualSubmit}
diff --git a/src/payments/contract_checkout.py b/src/payments/contract_checkout.py
index 96a485f1..a91a24ff 100644
--- a/src/payments/contract_checkout.py
+++ b/src/payments/contract_checkout.py
@@ -1666,6 +1666,168 @@ class PaymentContractCheckoutService:
         except Exception:
             return {}
 
+    def validate_intent_tx(
+        self,
+        user_id: str,
+        intent_id: str,
+        tx_hash: str,
+    ) -> Dict[str, Any]:
+        """Pre-check a tx hash against an intent before submission.
+
+        Returns a validation report with ``valid`` and per-field checks.
+        Does NOT mutate any database state.
+        """
+        self._ensure_enabled()
+        intent = self.get_intent(user_id, intent_id)
+        tx_hash_text = str(tx_hash or "").strip().lower()
+        if not (tx_hash_text.startswith("0x") and len(tx_hash_text) == 66):
+            return {
+                "valid": False,
+                "reason": "invalid_tx_hash_format",
+                "checks": {"tx_hash_format": False},
+            }
+        if intent.status not in {"created", "submitted"}:
+            return {
+                "valid": False,
+                "reason": f"intent status is {intent.status}, cannot validate",
+                "checks": {"intent_status": intent.status},
+            }
+        now = _now_utc()
+        try:
+            expires_at = datetime.fromisoformat(intent.expires_at)
+        except Exception:
+            expires_at = now - timedelta(seconds=1)
+        if expires_at <= now:
+            return {
+                "valid": False,
+                "reason": "payment intent expired",
+                "checks": {"intent_expired": True},
+            }
+
+        w3 = self._get_web3()
+        try:
+            receipt = w3.eth.get_transaction_receipt(tx_hash_text)
+        except Exception:
+            try:
+                w3 = self._get_web3(force_refresh=True)
+                receipt = w3.eth.get_transaction_receipt(tx_hash_text)
+            except Exception:
+                receipt = None
+
+        if receipt is None:
+            return {
+                "valid": False,
+                "reason": "tx_not_mined",
+                "checks": {"tx_mined": False},
+            }
+        if int(receipt.get("status") or 0) != 1:
+            return {
+                "valid": False,
+                "reason": "tx_reverted",
+                "checks": {"tx_mined": True, "tx_status": "reverted"},
+            }
+
+        tx_to = _normalize_address(receipt.get("to") or "")
+        is_direct = intent.payment_mode == "direct"
+
+        checks: Dict[str, Any] = {
+            "tx_mined": True,
+            "tx_status": "success",
+            "tx_to": tx_to,
+            "block_number": int(receipt.get("blockNumber") or 0),
+        }
+
+        if is_direct:
+            event_match = self._extract_direct_transfer_event(receipt, intent)
+            if not event_match:
+                return {
+                    "valid": False,
+                    "reason": "direct_transfer_not_found",
+                    "detail": "ERC20 Transfer event not found on token contract. "
+                              "Ensure you transferred the correct token to the receiver address.",
+                    "checks": checks,
+                }
+            event_from = _normalize_address(event_match.get("from"))
+            event_to = _normalize_address(event_match.get("to"))
+            event_amount = int(event_match.get("amount_units") or 0)
+            expected_receiver = intent.receiver_address
+            expected_amount = int(intent.amount_units)
+
+            receiver_match = event_to == expected_receiver
+            amount_match = event_amount >= expected_amount
+
+            checks["event"] = "Transfer"
+            checks["event_from"] = event_from
+            checks["event_to"] = event_to
+            checks["event_amount"] = str(event_amount)
+            checks["expected_receiver"] = expected_receiver
+            checks["expected_amount"] = str(expected_amount)
+            checks["receiver_match"] = receiver_match
+            checks["amount_match"] = amount_match
+
+            if not receiver_match:
+                return {
+                    "valid": False,
+                    "reason": "receiver_mismatch",
+                    "detail": f"Transfer went to {event_to}, expected {expected_receiver}",
+                    "checks": checks,
+                }
+            if not amount_match:
+                return {
+                    "valid": False,
+                    "reason": "amount_insufficient",
+                    "detail": f"Transfer amount {event_amount} is less than expected {expected_amount}",
+                    "checks": checks,
+                }
+        else:
+            event_match = self._extract_matching_event(receipt, intent)
+            if not event_match:
+                return {
+                    "valid": False,
+                    "reason": "order_paid_event_not_found",
+                    "detail": "OrderPaid event not found. "
+                              "Ensure the tx was sent to the correct receiver contract.",
+                    "checks": checks,
+                }
+            event_payer = _normalize_address(event_match.get("payer"))
+            event_order_id = str(event_match.get("order_id_hex") or "")
+            event_plan_id = int(event_match.get("plan_id") or 0)
+            event_amount = int(event_match.get("amount_units") or 0)
+            event_token = _normalize_address(event_match.get("token_address") or "")
+
+            order_match = event_order_id == intent.order_id_hex.lower()
+            plan_match = event_plan_id == int(intent.plan_id)
+            token_match = event_token == intent.token_address
+            amount_match = event_amount == int(intent.amount_units)
+
+            checks["event"] = "OrderPaid"
+            checks["event_payer"] = event_payer
+            checks["order_id_match"] = order_match
+            checks["plan_id_match"] = plan_match
+            checks["token_match"] = token_match
+            checks["amount_match"] = amount_match
+            checks["event_amount"] = str(event_amount)
+            checks["expected_amount"] = str(intent.amount_units)
+
+            if not all([order_match, plan_match, token_match, amount_match]):
+                failures = []
+                if not order_match:
+                    failures.append(f"order_id mismatch: got {event_order_id}, expected {intent.order_id_hex.lower()}")
+                if not plan_match:
+                    failures.append(f"plan_id mismatch: got {event_plan_id}, expected {intent.plan_id}")
+                if not token_match:
+                    failures.append(f"token mismatch: got {event_token}, expected {intent.token_address}")
+                if not amount_match:
+                    failures.append(f"amount mismatch: got {event_amount}, expected {intent.amount_units}")
+                return {
+                    "valid": False,
+                    "reason": "event_mismatch",
+                    "detail": "; ".join(failures),
+                    "checks": checks,
+                }
+
+        return {"valid": True, "checks": checks}
+
     def submit_intent_tx(
         self,
         user_id: str,
diff --git a/web/core.py b/web/core.py
index 6b246173..a8592cd1 100644
--- a/web/core.py
+++ b/web/core.py
@@ -376,6 +376,10 @@ class SubmitPaymentTxRequest(BaseModel):
     from_address: Optional[str] = None
 
 
+class ValidatePaymentTxRequest(BaseModel):
+    tx_hash: str = Field(..., min_length=10)
+
+
 class ConfirmPaymentTxRequest(BaseModel):
     tx_hash: Optional[str] = None
 
diff --git a/web/routers/payments.py b/web/routers/payments.py
index 6f55ed36..17173bd8 100644
--- a/web/routers/payments.py
+++ b/web/routers/payments.py
@@ -6,6 +6,7 @@ from web.core import (
     ConfirmPaymentTxRequest,
     CreatePaymentIntentRequest,
     SubmitPaymentTxRequest,
+    ValidatePaymentTxRequest,
     WalletChallengeRequest,
     WalletUnbindRequest,
     WalletVerifyRequest,
@@ -21,6 +22,7 @@ from web.services.payment_api import (
     reconcile_latest_payment,
     submit_payment_tx as submit_payment_tx_service,
     unbind_payment_wallet,
+    validate_payment_tx,
     verify_payment_wallet,
 )
 
@@ -67,6 +69,15 @@ async def payment_get_intent(request: Request, intent_id: str):
     return get_payment_intent(request, intent_id)
 
 
+@router.post("/api/payments/intents/{intent_id}/validate")
+async def payment_validate_tx(
+    request: Request,
+    intent_id: str,
+    body: ValidatePaymentTxRequest,
+):
+    return validate_payment_tx(request, intent_id, body)
+
+
 @router.post("/api/payments/intents/{intent_id}/submit")
 async def payment_submit_tx(
     request: Request,
diff --git a/web/services/payment_api.py b/web/services/payment_api.py
index eb6ebcd2..071545cd 100644
--- a/web/services/payment_api.py
+++ b/web/services/payment_api.py
@@ -11,6 +11,7 @@ from web.core import (
     ConfirmPaymentTxRequest,
     CreatePaymentIntentRequest,
     SubmitPaymentTxRequest,
+    ValidatePaymentTxRequest,
     WalletChallengeRequest,
     WalletUnbindRequest,
     WalletVerifyRequest,
@@ -155,6 +156,22 @@ def submit_payment_tx(
         _raise_payment_error(exc)
 
 
+def validate_payment_tx(
+    request: Request,
+    intent_id: str,
+    body: ValidatePaymentTxRequest,
+) -> Dict[str, Any]:
+    identity = _require_payment_identity(request)
+    try:
+        return legacy_routes.PAYMENT_CHECKOUT.validate_intent_tx(
+            user_id=identity["user_id"],
+            intent_id=intent_id,
+            tx_hash=body.tx_hash,
+        )
+    except legacy_routes.PaymentCheckoutError as exc:
+        _raise_payment_error(exc)
+
+
 def confirm_payment_tx(
     request: Request,
     intent_id: str,