Each preparer entered in your program must have a separate PTIN. The default preparer entry should be the practice owner. The practice owner must invite other preparers. If you have the person you're trying to invite actually set as the practice owner, this will produce a duplicate error. The invitation will look for a match of preparer name, PTIN, and SSN.
To determine which name is actually set as the practice owner in your program, start a new return:
To change the preparer entry for the practice owner and another preparer:
When the correct preparer is assigned as the practice owner, and as long as preparer name, PTIN and SSN are unique (not duplicated), you will be able to invite the other preparer.
When the other preparer clicks the link in the invitation, they can then use or create their own TaxAct account which will be associated with the practice. This will allow association of e-file records through the main practice ID.