Enter a valid partner number

What causes this issue?

The partner number '&v1&' does not exist for the partner type '&v2&'.

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?

Enter a valid partner number and make sure that this partner number
exists for the partner type.

Error message extract from SAP system. Copyright SAP SE.