Raspberry Pi Relay HATs are two a penny, but few come with a dedicated mobile app. Meet the PiRelay, a HAT that can manage up to 240 VAC/7 A or 125 VDC/10 A loads across four relays. The PiRelay costs US$17.06 via SB-Components, which ships worldwide.
https://www.notebookcheck.net/PiRelay-a-Raspberry-Pi-relay-shield-with-a-mobile-app-that-costs-just-US-17-06.425389.0.html