I think there are two key questions here: (1) Exactly what did the user pay for? If it's an app that promises to provide access to Twitter, then I'd think the

I think there are two key questions here: (1) Exactly what did the user pay for? If it's an app that promises to provide access to Twitter, then I'd think the app developer is responsible for making the necessary arrangements with Twitter to uphold that promise. If it's an app that promises to make a best-effort attempt to use Twitter's public APIs, then a refund doesn't sound reasonable. (2) Should the user consider this a simple business relationship, or something more personal? I.e., even if a case could be made for a refund, should that matter?