go to:

1. AP
2. Mail
3. forms

Once the Aatrix grid loads, in this case there would be two or more rows with the same tax ID. Once you select NEXT, the system will ask you if you'd like to combine into a single line, or keep the rows separate. To keep separate, you would have to find the column titled Account Number, and add a distinguishing number in each row (usually starting at one and moving sequentially, as needed)