Can i get some help here? What's wrong with this API call?

I’m logging in and testing it, and im affiliated, so it should not come up with this problem.
Although, if i make the URL one string with my twitch username in it directly, then it works.
Like this:

"channels/" + streamerName + "/subscriptions" - DONT WORK
"channels/MY-TWITCH-USERNAME/subscriptions" - THIS WORKS, AND I GET THE INFO