I was just there 2 weeks ago and what you do is get at least one picture. Doesn't matter if it's a photopass photographer or a ride photo. We actually had a Space Mountain ride picture as our first. I got the code from the screen and entered it into the app - make sure you're signed in on the mobile app with the same account you used to purchase the photopass. About 20-30 minutes later the picture was available in the app and there was now an option to activate our photopass. You won't see any change at all in the
Disneyland app until you have the option to activate the pass - it doesn't even indicate that you've purchased a photopass which I find a bit annoying.