Uauuu thank you for answer quick.
Do if i want t know if a channel A is subscribed to channel B i take the names of the two channels i do a getusers of both, I take the ids and i call this endpoint with the two ids
https://api.twitch.tv/helix/subscriptions/user?broadcaster_id=${ id1 }&user_id=${id2 }`
And it will work ??