Credit Memo not in 'AR_PAYMENT_SCHEDULES_ALL'

User created a credit memo that had to be applied to an invoice#.

CM header total = 0 , CM lines show -ve amount. Credit Memo has been completed. In Application screen I do not see the invoice record to which this CM was applied to.

So I tried to select the invoice #. and form gave me an error : "FRM-40738 - Argument 1 to builtin NAME_IN cannot be null"

checked the table AR_PAYMENT_SCHEDULES_ALL and the customer_trx_id is not found for that CM.

Invoice on the other hand shows : Total balance due as original amount. refund did not factor in.