How do I post a payment to tenant account who has been moved-out & debt been written off.

Sometimes you can go to a moved out account and add an Administrative Adjustment and take a payment on that.

I often can't get it to work on a unit that has had the charges written off.  In that case, the way I handle this is in the Daily Close.  Enter Ledger Adjustment.  Enter the amount with a memo about what unit it was from and what it was for.