You are absolutely allowed to expose access to end users, as long as you continue to abide by terms of service. We have hundreds, if not thousands, of apps built on openrouter that in turn have end users of their own. We showcase many of them on our /apps ranking page!
I was actually wondering about this since I've seen like 3 comments talking about the same thing, would it happen to be related to money laundering due to the availability of the crypto payment method?
TOS says: access the Site or Service for purposes of reselling API access to AI Models or otherwise developing a competing service;
So yes obviously you can do what you want as long as you abide by terms of service, but the terms of service does NOT allow you to resell the API.