fix(docs): correct status code and update pending trade lock behavior for /submit endpoint

fern/docs/pages/gasless-api/guides/gasless-api-technical-appendix.mdx

@@ -211,7 +211,7 @@ If the submitted trade is successful, and object with `type`, `tradeHash`, and `
   - (`otc` only) If the trade has been outstanding for too long.
   - (`otc` only) If the balance / allowance of the market maker selected to settle the trade is less than the trade amount (very unlikely).
   - If the query params are not able to pass validation.
-- `429` if there is already a trade associated with a taker address and a taker token that's not been settled by our relayers yet. For example, if `address A` already has a `USDC -> WETH` trade submitted and it has not settled yet, then a subsequent `/submit` call with `address A` and `USDC -> *` trade will fail with `429`. The taker is, however, allowed to submit other trades with a different taker token.
+  - If a pending trade already exists for the same taker address and sell token where the sum of pending sell amounts would exceed the taker's effective balance (the minimum of their balance and allowance).
 - `500` if there is an internal server error.
 
 ## Note for go-ethereum