Line item has incorrect Dr/Cr indicator for remaining amount

What causes this issue?

The remaining balance to be posted cannot be posted using the selected
posting key, since the debit/credit indicator does not match the
existing document balance.

System Response

The posting amount cannot be determined automatically.

How to fix this error?

Leave the amount empty, and enter a line item with appropriate posting
key.

Error message extract from SAP system. Copyright SAP SE.