Problems with SetAuthenticationPhoneNumber function

[a1ex33]

Hello.
We are having problems sending authorization codes.
Everything has been working fine for over a year, but recently some users have not received authorization codes.
The call to the SetAuthenticationPhoneNumber function is completed successfully and returns Ok.
We also receive the authorizationStateWaitCode event. But the code itself does not arrive to another authorized Telegram session.
What could be the reason?

[levlam]

It is up to the server how and when authorization codes are sent. Application can't affect this behavior.

[a1ex33]

It is up to the server how and when authorization codes are sent. Application can't affect this behavior.

Maybe there are some recommendations? What should I avoid and stick to? I've noticed that codes from official web versions are successfully sent to the same numbers.

[levlam]

I can't give any relevant recommendations.