See explanation below.
Explanation
You need to add a write-off reason for USMF and set it as the default.
Go to Navigation pane > Modules > Credit and collections > Setup > Accounts receivable parameters.
Click the Collections tab.
Click the Edit icon in the Write-Off section.
Add a new Write-Off reason if it doesn't exist.
Tick the "Default" checkbox next to the new Write-Off reason.
Click the Save button to save the changes.