The payer’s approval of specific services, a number of units and a date range. Work outside it is work you may not be paid for — and no amount of documentation fixes that afterwards.
Before the work, the payer authorises it: which services, how many units, and between which dates. In Ohio the MCO authorises against a written plan (the RH-45 is the request). In Washington the referral itself carries a cap. In Massachusetts the approved IWRP plays the same role.
Note the word: authorisation, not “prior auth” and not “pre-cert.” Those are clinical terms from a different system.
An authorisation for, say, forty units is spent a tenth at a time across weeks. What is left is arithmetic you are doing in your head while doing something else, and the moment you cross the line nothing happens — no warning, no rejection. You find out when the payment comes back trimmed.
That is the most preventable unpaid work in this profession, and the fix is not discipline; it is a running “authorised / used / remaining” figure per plan or referral, visible while you are logging the activity rather than reconstructed at month end.
The daily activity grid keeps the remaining units on screen as you type, and the state guides cover how each state authorises.
Fifteen minutes, your state’s codes on screen — or start the trial and poke around on your own.