I need add a second verification phone number for gmail but the verification for 1st phone number always failed.

Add backup phone number can but add second phone number verification always failed.
Always said too many ateempts or suspicious activity please try again later.
Been trying to do that for months now.

I dfidnt even spam emails to others so whats the problem?
Is it someone attemnpt to hack into gmail?

Outlook mail you can check for activity but gmail how to check?