For this invoice observations are mandatory (see long text)

What causes this issue?

Invoices for 3rd parties, consignment, RTP, subcontracting expects
observation text.

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

System Response

How to fix this error?

Please maintain the text field in the creditor screen. Select the first
item in the overview screen.

Error message extract from SAP system. Copyright SAP SE.