Using the official Apple Pay JS SDK (https://applepay.cdn-apple.com/jsapi/1.latest/apple-pay-sdk.js), the onvalidatemerchant event returns the validationURL: https://apple-pay-gateway.apple.com/paymentservices/startSession
Our server performs merchant validation via mTLS using exactly this URL, with a valid Merchant Identity Certificate, and Apple responds with HTTP 400 Bad Request.
Apple's current documentation instead references /paymentservices/paymentSession and states that "Start Session is being phased out and replaced by Payment Session". Since the URL is provided by Apple's own SDK, is startSession still valid when returned by onvalidatemerchant, and why is it rejected with 400?
Anyone is experiencing this?