WeChat Pay APIv3 Integration in Practice: Signing, Callback Verification, and Idempotency
WeChat Pay APIv3 rewrote the signing algorithm, the certificate model, and callback encryption all at once, so patterns carried over from v2 fail reliably. This walkthrough follows the real integration order: what each of the three key materials does, how to compute a request signature, how to verify and decrypt callbacks, which of the four payment products to pick, and how to build the order state machine and idempotency.