VOIP Notification not received in iOS Device either Sandbox or Production

Hi I am working with Applications which require VOIP functionality. I do have valid VOIP certificates. I have tried sending notifications from the Houston App, Pusher App, Backend service which make use of a PHP Script.

But no notification is received in the device. I installed application using Testflight and used the token and also tried the app by installing it directly by the Xcode on a real Device. Running latest OS 14.6 and Xcode, macOS are also updated to the latest.

Token is valid, Certs are valid and also installed in the keychain, PEM file are also okay I checked using SSL commands. I also tried creating new certificate also still no positive response.

Please suggest.