In my understanding by "paying royalties" means paying only artist (singer/producer/engineer etc) involved in the creation of the song, so it means only megan will receive the royalties as one of the singer + other artists involved (including BTS). Since megan's label was not involved in creation they will get none, and it depends on the contract of megan with her label how much megan willing to share her income (from the royalties she receives) with her label.
Megan signed her contract when she was a nobody and has a horrible contract, she's been fighting with them for a couple years now. I don't know the %, but 1501 gets at least 50% of her royalties, as they get over 50% on literally everything she makes music wise
