I have a customer always failed in verify app, the situation is like the bottom description of https://support.apple.com/en-us/HT204460 (status is keep "Not Verified", and tap "Verify App" always get "Unable to Verify App" alert.)
The weird thing is: other customers and I all can pass the verify app, is the same ipa file, and certificate is still validate and no revoke.
The alert says need internet connection is required to verify trust of the developer... but according to Apple document, the connection server is https://ppq.apple.com and it always display "Http/1.1 Service Unavailable" no matter on the app can be verified or cannot. So the problem is I cannot understand the root cause when verify app failed or how to fix it.