None!
Myndstream for Spa has been designed end-to-end for use in spas so once you purchase the subscription you're good to go. Whether you're in the US or UK or elsewhere around the world you do not need a separate public performance license to play music from our website in your spa setting.
Please note: these licences do not cover you performing any of the music, content or related content outside of the website service. Full T&Cs are here.