When defining a user-defined action, you can expose it as a function that can be used in your application module expressions. In this context the action will also be recognized as a User Function and will also be available for use, like any built-in function, in the Scope tree of the Expression editor.
You cannot define a user-defined action as a function when:
The action has no output parameters
The action has more than one output parameter
The action has the same name as a built-in function
In a case where name clashing occurs, Service Studio automatically renames your action. Learn About elements naming.
If, at design time, you try to perform a change that would cause violations 1 or 2, Service Studio prevents it, but allows you to automatically change the action to meet the requirements to be a function:
By creating an output parameter, if the action has none and you're trying to set the property Function to Yes.
By setting the property Function to No, if you're adding another output parameter to a User Function.
By setting the property Function to No, if you're deleting a User Function single output parameter.
Be aware that the above automations may invalidate your eSpace in a case where you're using the User Function.
Use User Functions | Action Properties | Expression Editor