Quantity Conversion Interface: Field OIB04-FMTYP: & not in range

What causes this issue?

An invalid Function Module type has been entered.

How to fix this error?

Enter a valid function module type.
1 = ABAP/4 function module (Do not use for new conversion groups
designed after Release 4.0B)
2 = Customer exit routine (also ABAP/4) (Do not use for new conversion
groups designed after Release 4.0B)
3 = Call System
4 = Remote Function Call (RFC)
5 = ABAP/4 function module (NEW)

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

Error message extract from SAP system. Copyright SAP SE.