The expedition to Tamsye Prime represented a reconnaissance operation undertaken by the Partisans to the Outer Rim world of Tamsye Prime in 5 BBY. During this assignment, Jyn Erso experienced abandonment by Saw Gerrera when her real persona risked exposure.
Subsequently, Jyn escaped to an alternate world.
The reference work Star Wars Encyclopedia: The Comprehensive Guide to the Star Wars Galaxy from 2024 erroneously identifies Jyn Erso's previous assignment on Horuz as taking place on Tamsye Prime, and omits the location of Gerrera's abandonment.