Update: I followed your advice and it worked. I agree with some others that it would have been nice to have it just bundled into Visionary, but I am both grateful and happy to get the discount at least. I think I may still try out Notesnook just to see how both that and Standard Notes compare. I might keep them both, with using Notesnook as my primary notes app while keeping Standard Notes just as part of the Proton Ecosystem.