No partner for partner function &2 exists for supplier &1

What causes this issue?

You wanted to determine a partner with partner function &V2& for vendor
&V1&. However, no partners are entered in this partner function for
this vendor.

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?

Create a partner in the partner function for the vendor.

Error message extract from SAP system. Copyright SAP SE.