Hi NAV Enthusiasts,

As a simple rule, it's known to everyone that a negative amount cannot be applied to a negative amount in NAV or Business Central.

It means that we cannot apply a Sales Credit Memo to a Customer Payment (Payment received from the customer).

 
But, Let me tell you that it's not completely true. We can apply Sales Credit Memo to a Customer Payment (Payment received from the customer) despite both having -ve amounts.
Watch the complete video to know how it happens:
Hope it helps! Cheers!