I got this earlier today:
Method: messages.sendMessage
Url: N/A
Result: {"_":"rpc_error","error_code":400,"error_message":"USER_BANNED_IN_CHANNEL"}
Stack: Error
at Object.h [as invokeApi] (https://web.telegram.org/js/app.js:23:25735)
at Object.Z.l.send (https://web.telegram.org/js/app.js:29:5996)
at https://web.telegram.org/js/app.js:15:7420
at t (https://web.telegram.org/js/app.js:13:2586)
at a (https://web.telegram.org/js/app.js:15:17764)
at g.$eval (https://web.telegram.org/js/app.js:13:12666)
at g.$apply (https://web.telegram.org/js/app.js:13:12899)
at HTMLAnchorElement.<anonymous> (https://web.telegram.org/js/app.js:15:17816)
at HTMLAnchorElement.dispatch (https://web.telegram.org/js/app.js:4:2788)
at HTMLAnchorElement.f.handle (https://web.telegram.org/js/app.js:3:31557)