iOS is not receiving push notifications via APNs newly created app using p12

Hello Apple Community,

I'm writing to seek your help in resolving an issue that I have been experiencing with push notifications on my newly created iOS app.

Recently, I have created another new app from app store connect with push notification settings enabled using P12 certificate (Production & Sandbox SSL certificate) and it is in TestFlight not yet in app store.

In that, I am not receiving push notifications from APNs. From the backend that has successfully sent responses to iOS using device token. But from the app side not receiving the push notification. Despite having enabled the notifications in the app settings.

I have tested using the Push Hero Mac app by sending push to my app using P12 certificate, Bundle id, Device token and Message and app receiving the push successfully. But not receiving push while sending from backend server developed using c#.

Same settings working fine in another app and that push notification was working fine using the p12 certificate.

So I have replaced the existing app p12 certificate to the newly created app from the backend to send push notification and it is working fine.

I have used below details:

Certificate: Production & Sandbox SSL Certificate

Port: 2195

gateway: gateway.push.apple.com:443

Mode: Production

I have also tried restarting my device and force-quitting the app, but the problem persists. I am not sure what else to do at this point, and it is becoming increasingly frustrating to miss important updates and messages.

I would appreciate any advice or solutions that you can offer to help me troubleshoot this issue. Has anyone else experienced this problem before, and if so, how did you resolve it?

Thank you in advance for your help.