Only input fields can be required entry fields. Operation not performed

What causes this issue?

You attempted to assign the attribute "Require field" (obligatory
output) to an input/output field, but the "input field" attribute is
not set.

System Response

Invalid attribute combination rejected.

How to fix this error?

if you want to assign the "Required field" attribute, you must first
assign the "Input field" attribute.
Not all templates can be input fields. Fields to which an icon is
assigned can only be output fields.

Error message extract from SAP system. Copyright SAP SE.