What it is:
Box 1a is where the insured's ID number is entered as shown on their ID card for the payer to which the claim is being submitted.
Therabill will use the value that is entered into the Primary ID field for the insurance card.
On the top menu bar, select Clients / Client List. Click the blue pencil for the desired client. Click Add Card or the blue pencil of an existing insurance card. You will now see the Edit Insurance Card form. In the Policy Info section find the Primary ID: field and enter the appropriate value.