Alipay configuration error codes: ILLEGAL_PARTNER_EXTERFACE and ILLEGAL_SIGN

First, confirm you are subscribed to both PC Website Payment and Mobile Website Payment. A missing subscription for either service will cause payment errors.

On the Alipay Open Platform, go to the product subscription management page to confirm that both services are listed as Active. Next, ensure you obtain your partner ID (PID) and key from the correct location. Sign in to b.alipay.com and go to the "Account Management" page. From there, find "Merchant Information Management" and click "View PID|KEY". This displays your 16-digit partner ID (PID), which starts with 2088, and your 32-character MD5 key. Credentials from the Ant Financial Open Platform will not work for this configuration; you must get them from b.alipay.com. Alternatively, on the key management page in your Alipay Account Center, select MAPI gateway product key from the left navigation pane. In the partner key area on the right, find the MD5 key row and click View to see your key.