Set Return Value not working properly

I have a function that uses the set return value action. Strangely, everything in the code seems to work as intended, except for the return value function. The debug text object always displays "???" and when I remove that line, it displays "" (i.e. an empty string) regardless of the outcome.

The image below contains comments, which should make it clearer.

I may be missing something, but if the set opacity events are triggering, surely the set return value ones should be as well?

You are using wait inside the function. The parent event where you call the function won't wait for it to finish. That's why it displays "???"

If you need to wait for the function to complete, it needs to be set as asynchronous. And asynchronous functions can't return a value.

You can do this: