Use AP > Tasks > Change Invoices to edit the distribution line to add the commitment.

For paid invoices, it's best to use Change Invoices and add new lines of distribution: a distribution for negative amount coded the same as the original distribution to "reverse" it, then a distribution for positive amount that is coded to the commitment. Then a 0.00 payment will need to be recorded to pay the new distributions. Sage Knowledgebase article 17493 How do I change distribution information on a paid Accounts Payable invoice? covers this in more detail.

April Dahlthank you!  That's what I thought I was supposed to do but I couldn't remember!