Tax on sls/purch.gp & has already been assigned to comp.cd & with ctry &

What causes this issue?

The tax on sales/purchases group in question has already been allocated
a company code with a different country key to the company code
which you are now attempting to allocate to the group.
All company codes allocated to a tax on sales/purchases group must have
the same country key.

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.