1.

Have you run the integrity check per the other thread you commented on? :

"Run the Data Integrity and see if that reports anything.
Usually this is a discrepancy between the AP Documents and the Open Document Details."

2.

And have you reviewed this ? :

https://www.sagecity.com/support_communities/sage300_erp/f/sage-300-financials-suite/52364/over-application-error-posting-a-p-adjustment