Arianna Grande recently performed the 'Rift Tour' for Fortnite, which lasted about 12 minutes. Moist Cr1tikal, or Charlie to his fans, stated that it was the easiest paycheck she had ever received. It's a pretty compelling argument, to be honest, and Ariana Grande didn't even have to attend the event and earned money.
This wasn't a live concert, just Fortnite using Ariana Grande's likeness and three of her songs. From what I could see, Ariana Grande was not directly involved in any of it beyond giving her the go-ahead. In that respect, Moist Cr1tikal is correct, and it really doesn't get any easier than that.
Ariana Grande received an easy paycheck from Fortnite, according to Moist Cr1tikal
Fortnite hosted the Rift Tour of Ariana Grande on August 6. In addition to bouncing, players could fly and ride unicorns while Ariana Grande's music played. Though the experience was not all that extraordinary and not many people thought it was the best thing ever, it was still nice to have.
Start at 6:46 for Charlie's thoughts (As noticed by Dexerto)
To quote Moist Cr1tikal:
"That had to be the easiest paycheck of her life. 'Hey, can we call this a concert for you, Ari? We're just going to use three of your songs for an event in Fortnite?' 'Yeah, that's fine…' It was very pretty, though. I don't have any complaints about it other than it was literally three songs."
Despite Charlie's disappointment, the majority of gamers seemed to enjoy the game. Even though it was short, it was still an event, and Fortnite just wanted to do something for their fans. Arianna Grande certainly has nothing to complain about.