Basic 23 is really frustrating

So I've been trying to crack this challenge on and off for weeks now and I'm still not making any progress, I've read up on what RFI is, but I cannot for the life of me figure out what this challenge wants. I've tried to look into how to exploit the vulnerability, it's just that any tips I find on this site or in articles seem to lead to dead ends. It's particularly annoying because I know that it wants a c******, but I cannot figure out how it wants me to inject it at all. I really need some guidance here

Since it's an RFI exploit I expect what this challenge wants is a file from somewhere else.

It doesn't want a c****** either, whatever that is, it wants a s****.

And you dont need to inject anything you just need to tell it where your s**** is located.