Hollow and Venom by Amelia MacLeod

Fake courtesan. Real feelings. Impossible odds. Some lies are worth dying for. Neve has spent her life hiding a deadly secret: she's immune to the magical thrall that controls every other human in the Vales. When her defiance catches the attention of Prince Sylvan Everstone—the notorious Soulslayer—she expects torture or death. Instead, he claims her as his courtesan to save her life. It's a lie that could get them both killed, but it's also her only protection from a court of sadistic mages who see humans as disposable playthings. Forced into an intimate charade with the realm's most dangerous man, Neve must navigate deadly court politics while hiding the truth about her immunity. But darker forces are stirring. The mage king has plans that go far beyond simple cruelty, and the ancient ritual that could seal his schemes draws near. As the kingdom hurtles toward catastrophe, Neve faces an impossible choice between the safety of shadows and stepping into a light that could either save her people—or destroy them all. A steamy enemies-to-lovers fantasy romance featuring a morally gray hero, a fearless heroine with hidden powers, and stakes that could reshape the world.