In correct.
Get User Subs doesn’t work with a user token to get the subscriptions a user has.
You have to use v3/v5 to get the subscriptions a user has.
Get User Subscriptions
Gets broadcaster’s subscriptions by user ID (one or more).
Get User Subs lets you perform a broadcaster_id/user_id key search when you have a broadcasters token.
OP specifically asked about subscriptions a user has. Which is NOT in Helix