Balance in &1 is not zero, posting not possible

What causes this issue?

You are attempting to post a document for which the balance is not zero
in one or more currency.

System Response

During online processing:
Error message requiring a correction.
During background processing:
Error message causing processing to be terminated.

How to fix this error?

When working online:
Correct the line items entered. If the amounts entered balance to zero,
and this error message still appears, there is a program error. In this
case, treat the error as if it occurred during a background processing.
Background processing
INCLUDE NA_SYSADMIN1 OBJECT DOKU ID TX

Procedure for System Administrators

INCLUDE FICA_NA_OSS OBJECT DOKU ID TX

Error message extract from SAP system. Copyright SAP SE.