Yes the party ticket must be linked to a different account than the normal account. You also need to have RFID media for the party tickets. We did this with
MNSSHP tickets but I ordered paper tickets instead of RFID cards so I could book FP+ but had no way of using them in the park.
I made shorted versions of our names as the other accounts and and attached the Tickets to the party to that. It would have worked if I had asked for the correct cards. The FP+ passes would only be usable from 4-7PM. Once the party starts FP+ is not used.