GTD number &1 already exists in database table

What causes this issue?

The number selected by the system from the maintained number range
interval is already used. It should be unique.

System Response

The system automatically stops invoice splitting and combining.

How to fix this error?

Check the settings of the number range interval for the object
<AB>GTICHINA</>.

Procedure for System Administrators

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

Error message extract from SAP system. Copyright SAP SE.