[5] On 27 January 2019, Foster joined USL Championship side Rio Grande Valley FC Toros on loan.
[6] Foster joined Costa Rican side Santos de Guápiles on loan following the end of his spell at Rio Grande Valley.
[11] He made his first appearance for the club the next day on 24 August in a 2–3 away loss to Las Vegas Lights FC, replacing Jack Blake at halftime.
[12] Foster scored his first goal for the Indianapolis-based club on 14 September in a 3–1 home win over El Paso Locomotive FC.
[17] Foster made his senior team debut on 30 January 2018, in a friendly match against South Korea in Antalya, Turkey.