If you are trying to get OTP from PNB bank then you should confirm these points below.
1. Google pay should be in the latest version. If the version is not updated then first update your Google pay app.
2. Check your registered mobile number registered with PNB (Punjab National Bank ) bank.
3. PNB Bank can take several times because this is a very busy schedule. May be server busy or connection weak. Try after 24 hrs.
4. Check your mobile number balance for upcoming messages. You should have an active incoming plan on your mobile number.
I hope, these points will be helpful.