UPSET PAY MY DOCTOR: WHERE'S MY CLIENT ID?

Okay, right, I need to cover my doctor's invoice. I went the system and it says I need a account number. But, I don't have that! What am I supposed to check? Is there a way to retrieve my client ID? Can someone figure this out. It's really annoying having to stop payment because of this. Veradigm & Pay My Doctor: A Guide Navigating healthcare ex