Why these tropes fit

An unwanted arranged marriage forces an heir and a rebel leader into close proximity. She hides her dangerous work behind masks while using the marriage for access, and his discovery of her secrets forces both to choose between loyalty, survival, and the passion growing from their hostility.

Evidence from the source

Arranged Marriage: “his father arranges a quick, quiet betrothal with someone far beneath his station.” source
Enemies to Lovers: “The Flame and the Forsaken is an enemies to lovers, female Robin Hood fantasy romance” source
Forced Proximity: “leaving them shipwrecked, battered, and fighting for their very survival.” source
Revenge Plot: “They work under the subterfuge of darkness and masks, slowly taking back everything pilfered from their people.” source
Marriage of Convenience: “But her repulsive marriage affords her something they could never obtain on their own. Access.” source
Sacrifice: “she does something drastic to save her friends from the scaffold.” source
Heist: “This next job could change everything, but if they fail, she and her five friends—including her beloved brother—will hang.” source