Sure, in your case because you designed it that way.

I can imagine a service that queries some data from another service as _part_ of the end result, but the user is hitting your endpoint.

Anyway, what you *can* do with nostr is hitting any service with *any* pubkey - meaning you can decide to pay for your users or make your users pay for it directly, or some other clever combination.

IP addresses don't give you that freedom - it is not a good idea to use them as identity on the internet, so you see most paid services requiring an account.

Nostr could be that account.