Variable trigger doesn't work

Hi,

I have a project with a slide which is the main menu. There are 3 buttons that send the learner to different interaction slides (right now there are 2, the project isn't loaded or heavy). I want the learner to have access to the second interaction only after they've finished the first one, etc.

I created a variable that changes when the learner clicks the "continue" button at the end of the interaction, and a trigger that needs to change the button in the main menu from "disabled" to "normal" (and the first button to a "completed" state) when the variable changes.

the trigger won't work, the variable doesn't work between different slides.

I tried to add a variable inside the slide master (a numeric entry' that I placed outside of the screen). When I did this the project didn't run correctly at all (not in preview and not in the published project) - at the end of the first interaction, when clicking "continue", the project got stuck and didn't return to the main menu slide (it looked like it's loading, but it was stuck and never finished loading). I deleted the variable in the slide master and the problem disappeared.

But I still need a solution to how to make the second interaction button available in the main slide only after the first one's completed. Any ideas how to solve this, or as to why the variable doesn't work between slides?

thank you!