@Sara83 This happened to me once and, if you search around here, a lot of people have had this issue - and the weird thing is there doesn't appear to be one simple fix. I had it about two years ago, contacted support, they scratched their heads for a couple of days and then it was fixed. I don't know what they did, or if in fact they fixed it or it fixed itself. The annoying thing was that my response rate was affected and they just shrugged.
I get all the notifications possible - app, text, and email - but when the app stopped working, the texts stopped, too, so that wasn't much use.
Anyway, if you haven't already, send a message to @airbnbhelp on Twitter and see if you can get them to fix it.