Hi! Glad you like it. Let me know if you try it out. I’d like to hear how it goes!
Yes, I have been playing that you can immediately spend XP as soon as it is earned. But you can still only ever spend XP to turn a die into a six for the purposes for advancement. So the only time you should be able to spend XP directly on the failed roll you gained it for would be for Do Anything 1. (Or some other 1 die skill.)
I hope I explained that well. Let me know if it doesn’t make sense.