List of objects with 1 property from variable?

How to add “list of objects with 1 property” from variable?
I need to add information to a combo box from a rest service, I have been trying to add it from a variable but I have not succeeded, any suggestions?

Error to add variable!

No one answered, I guess no one understands the problem and what you are trying to do.
Please share screenshots of the logic flow you’re trying to build.