Nekogram のテレグラム投稿

In the latest Telegram Android, the Telegram server may request the client to do a Play Integrity check at any time with error code INTEGRITY_CHECK_CLASSIC_X, then the client will perform a Play Integrity check and resend the request with the invokeWithGooglePlayIntegrity method.

TLDR: Telegram can check whether you are using genuine Telegram app on a "genuine" Android device at any time while you are using the app.

Here is some explanation:

Your notification is delivered to your phone with FCM(Firebase Cloud Messaging), by the Telegram server sending notification with API Key coresponded to the App.
We third-party App developers are using the App configuration page on my.telegram.org to configure the API Key for our client.
However, the old FCM API was deprecated last year and will be removed soon, and Telegram still hasn't updated its configuration page(which received no update for 10 years) to reflect the API changes.