About Licence and producer name of my buyed song

Hello everyone. I have two urgent questions. I would be very glad if you answer

1-Under which license should I buy the music for my game? After all, I cant know how many copies it will sell.

2-I would be glad if you inform me about the subject of writing the name of the producer of the music I purchased in game jeneric.

Hello;
You can check all about license here;