Cannot change because multiple addresses with external number SPACE exist

What causes this issue?

There are multiple addresses for the business partner in which the
external address number was not entered. As a result, you cannot use
direct input to change these addresses.

System Response

Error message: the change copied is not carried out

How to fix this error?

Change the business partner in the SAP system (online) and enter the
external address number for the addresses. You can then change the
addresses by specifying the external address number or by using direct
input.

Error message extract from SAP system. Copyright SAP SE.