EU indicator correctly set for output tax ?

What causes this issue?

The EU indicator is used to classify the tax codes for the EC sales
list. Only postings with output VAT (taxes on sales/purchases) are
generally taken into consideration. In several EU countries, however,
postings with acquisition tax (input VAT) also have to be reported. An
EU indicator for the acquisition tax code only makes sense in such
cases. The EC sales list must, however, be carried out with a modified
version of the program in such cases, since a transfer of the VAT
registration number into the document does not currently take place in
the standard system when posting to vendor accounts.

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?

Error message extract from SAP system. Copyright SAP SE.