Kingdom of Lies (4 book series) by Stacia Stark

In Eprotha, magic is sacrificed to the gods in return for protection from the vicious fae. Wielding forbidden power is punishable by death.
When Prisca’s magic is discovered, she must flee her tiny village and ally with a ruthless mercenary and his lethal friends. The mysterious, arrogant mercenary forces Prisca to confront truths about herself––and her magic––that will reshape the future of the four kingdoms.
Truths that will lead to war.