Nightmare For Hire by Morgan Lysand

Nox is a Nightmare, literally. Having been around for eons, he’s decided it’s time to have some fun… wrecking lives, that is. So he hires himself out to get revenge on bad exes, which leads him to joining the Monster Match app. He doesn’t exactly care what the circumstances are as long as he gets to have some fun scaring humans.
Cyrus moved to Rivenfield for a fresh start after a bad breakup. He just wants to keep his head down and work. Maybe meet a few monster cuties on Monster Match. He’s not expecting to click with someone so soon, but the mysterious Nightmare has him all hot and bothered awake and asleep.
After meeting Cyrus, Nox is flabbergasted why anyone would want to send a Nightmare after such a delightful human. He becomes determined to get to the bottom of this mystery. It looks like the cure for his eternal boredom might just be falling in love.