Customer & is not defined for sales from &

What causes this issue?

No country-specific data has been created for the delivering country.
Country-specific data means above all tax classifications. The
delivering country is determined from the plant for the item.

System Response

The system does not permit entries for plants for which the country of
the sold-to party is not maintained, because no taxes can be
determined.

How to fix this error?

Check whether you can enter another plant for which the necessary data
has been maintained. If not, you must maintain the country-specific
data for the customer.

Error message extract from SAP system. Copyright SAP SE.