Balance not zero: & debits: & credits: &

What causes this issue?

The document balance is not zero. Therefore you cannot post the
document.

How to fix this error?

Depending on the reason for this balance, you can
correct invoice items
To do this, choose <LS>Edit</> --> <LS>Overview</> --> <LS>Adjustment
on/off</>.
post the difference to an account
To do this choose <LS>Edit</> --> <LS>New item</> --> ... and enter the
relevant account and the amount.

Error message extract from SAP system. Copyright SAP SE.