You can only use LIKE and TYPE to specify types in RFC

What causes this issue?

At the moment RFC only allows parameter types defined with LIKE and
TYPE. Other type categories such as TYPE REF TO are not supported for
RFC-compatible function modules.

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?

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.