I am the newbie in App Engine so I have some confusion about it. When I deploy my service to App Engine it default has SSL because I see the API link has https "https://abcdefgh.r.appspot.com/". I didn't config anything on SSL of App Engine.
When I build the Android App call to that API some devices can but some others can not, my customer can not but my phone can, so I can't reproduce the problem, and the error is java.security.cert.CertPathValidatorException
Please help me how can I solve it or any way to check it? why it just happened on some devices? Do I need to config SSL on App Engine or Android App?
On Android, I am using the Coroutine and OkHttp to make request.
Thanks so much.