You cannot delete the first entry. Overwrite it instead

What causes this issue?

You have entered several document numbers in the multiple allocation
area in <LS>More allocation criteria</> and are trying to delete the
first entry.
This is not possible.

System Response

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

How to fix this error?

You can only overwrite the first entry and delete the subsequent
entries if necessary.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.