Company is defined through master record, change not possible

What causes this issue?

For the used document type, it is determined that the company ID must
be the same for all line items. From the master record of one of the
accounts dealt with up to now, a company ID has already been
transferred to the document.

System Response

The manual entry of a company ID is not allowed.

How to fix this error?

If all entered accounts are correct, you can only post the document
via a document type with which the company ID can be predefined manually
and it must not be identical for all line items.

Error message extract from SAP system. Copyright SAP SE.