No VAT registration numbers are allowed for down payments/requests

What causes this issue?

You entered a tax code for a down payment or down payment request which
is defined as an EC tax code. This is not permitted, since this posting
is not subject to EC tax. A tax statement requirement exists upon the
delivery of goods to a foreign EC country, but not, however, upon
receipt of the down payment.

System Response

The system does not allow the tax code.

How to fix this error?

Use a different tax code or EC-identifier.

Error message extract from SAP system. Copyright SAP SE.