Hi there, bittersweetpetre.
If you already have a payroll subscription activated in QuickBooks Online (QBO), then you're able to add a user without upgrading the account.
You can follow these steps to add a user with payroll access:
Then, let the user know to accept your invitation.
I'm linking some of our great resources about payroll:
Let me know if you have any follow-ups and other questions. I'm here to help. Have a good one.