All parameters require a reference field or a type

What causes this issue?

You have defined a parameter without either reference field or type in
an update function module. This is not supported.

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?

You must assign either a reference field, a reference structure or a
type to each parameter.

Error message extract from SAP system. Copyright SAP SE.