The comments here were useful in getting yummy QR codes that work. Choose default option as advised, QR codes generated with Option 1 do not work. Once the trouble shooting is out of the way (app is in beta), these QR codes are a dream come true. I chose the prompt 'coffee' and every render is oh-so-aesthetically-pleasing. Burnt up the limit of 20 generations while figuring out what's going on. Use URL shortener, it doesn't process long URLs (understandable because it's mixing art plus readable info). Leave out https:// and www (the app told me, but I didn't believe it). Since I have two AppSumo accounts, that saved the day. Getting QR Diffusion free as an AppSumo user is just so awesome for visually oriented creative professionals.