Error changing invoice document & / &

What causes this issue?

The invoice document could not be changed.

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?

If you changed other invoice documents, save these now if you have not
already done so.
In the Invoice Verification comparison overview, refresh the screen to
read the invoice document again.
If you continue to have problems processing this invoice document,
contact your system administrator.

Error message extract from SAP system. Copyright SAP SE.