In RFC modules, only parameters with pass by value are allowed

What causes this issue?

You have defined a reference parameter for a remotely called function
module. However, only value parameters are allowed in this kind of
function module.

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?

Change the reference parameter to a value parameter.

Error message extract from SAP system. Copyright SAP SE.