Function module &1 for RE-FX does not exist

What causes this issue?

Function module &v1& does not exist.

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?

Make sure that application Real Estate (RE-FX) is installed correctly.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.