Customers with same VAT registration number found - check required

What causes this issue?

Customers with the same VAT registration number were found.

System Response

Information message and display of customers with the same VAT
registration number.

How to fix this error?

Check your entries.
The dialog box that appears displays the customers with the same VAT
reigistraion number. Using the "Cancel" function, you can return to the
screen that called up these customers. You can then bypass this check
using the function "Continue".
INCLUDE 'CUSTOMIZED_MESSAGE_INFO' OBJECT DOKU ID TX

Error message extract from SAP system. Copyright SAP SE.