Radio button group has only one parameter

What causes this issue?

You have used the extra function 'RADIOBUTTON GROUP <grp>' to determine
a group of radio buttons. A group of this kind must have at least two
elements. Only one element has been created.

System Response

The element has been created.

How to fix this error?

You must determine at least one more parameter in this group before the
system is able to generate the InfoSet.

Error message extract from SAP system. Copyright SAP SE.