I can’t dedicate much time atm, but just to give you a quick response to go off:
Except for the few APIs listed in this post, you are unable to access Roblox endpoints from within a Roblox Server. Attempting to will always result in the request erroring (which is what I believe is happening for you right now).
To get around this, you need to find a proxy which supports the endpoint you want. There should be a few listed on the devforum that you can try.