Hey @rmochette ,
Thanks for coming to the Community.
You'll need to make sure that your account's country setting is set to the same country as his account (Luxembourg). Once that's been set, you should be able to join the Premium Duo plan.
https://support.spotify.com/article/country-region-settings/
Let me know how it goes 🙂
Hey there you, Yeah, you! 😁 Welcome - we're glad you joined the Spotify Community! While you here, let's have a fun game…