docs: sync with docs.polymarket.com - 2026-05-21

docs/api-reference/trade/post-a-new-order.md

@@ -76,6 +76,7 @@ paths:
                   owner: f4f247b7-4ac7-ff29-a152-04fda0a8755a
                   orderType: GTC
                   deferExec: false
+                  postOnly: false
       responses:
         '200':
           description: Order successfully processed
@@ -168,6 +169,11 @@ paths:
                 error: could not insert order
         '503':
           description: Service unavailable - Trading disabled or cancel-only mode
+          headers:
+            Retry-After:
+              description: Seconds to wait before retrying when provided by post-only mode.
+              schema:
+                type: integer
           content:
             application/json:
               schema:
@@ -185,6 +191,14 @@ paths:
                     error: >-
                       Trading is currently cancel-only. New orders are not
                       accepted, but cancels are allowed.
+                post_only_mode:
+                  summary: Post-only mode
+                  value:
+                    error: >-
+                      post-only mode: only post-only orders and cancels are
+                      allowed
+                    code: post_only_mode
+                    retry_after_seconds: 79
       security:
         - polyApiKey: []
           polyAddress: []
@@ -218,6 +232,12 @@ components:
           type: boolean
           description: Whether to defer execution
           default: false
+        postOnly:
+          type: boolean
+          description: >-
+            Whether the order must rest on the book and not match immediately.
+            Only supported for GTC and GTD orders.
+          default: false
     SendOrderResponse:
       type: object
       required:
@@ -272,6 +292,12 @@ components:
         error:
           type: string
           description: Error message
+        code:
+          type: string
+          description: Machine-readable error code, when provided
+        retry_after_seconds:
+          type: integer
+          description: Number of seconds to wait before retrying, when provided
     Order:
       type: object
       description: >