@yigit.aybey , You Should assign the Default Value in the Variables Section for both the variables, then you should be able to Validate the Selectors if the Ui Element has the corresponding attribute values.
This error can also occur when you have more than one open from the same attachment screen.
Is another screen open with the screen title you introduced?
If it’s on, try to turn it off and define it again. If it needs to stay open you need to add cls to the selector.