Licence Question concerning Song for multiple Videos for Training App

Hey Guys, I have to buy some background music for some videos I’m editing. The videos will be published in a sports trainings app. My question is now which licence I have to buy. In total its about 30 Videos I’m doing, same project, same app, the videos will all look the same except for their slightly different contents. If I’m using the same song in every video, do I have to pay for every video then or do I pay once and can use it in every video because it belongs to the same project? Which licence do I have to get?

Thanks for your time! Really want to be sure on that one.

Many thanks in advance! Chris