People keep saying this but it didn't matter. I would turn it off on my wife's iphone and it would still say "you need to go back online in xx days" again, it's the spotify app in the iPhone settings. Make sure you have cellular data turned on.
No matter what platform you use whether it be Apple Music or Spotify, you’re going to run into issue. What I try to do is isolate the issue and use the forums to solve the dilemma. In your case it could be a matter of just uninstalling the application and re-downloading it.
I have always had this same problem as well. Everything works fine one moment and the next it tells me I'm offline It happens with WiFi and with cell data. This isn't a provider problem, or a WiFi problem, or a firewall problem... This is a Spotify problem. When all other services using internet work just fine and only 1 thing can seem to figure out you have an internet connection the answer is obvious, that 1 thing has a problem... It this case that 1 thing is Spotify. The app has numerous issues and none of them have been made better in the years I've been using the service. Literally the only thing keeping me around is the daunting task of rebuilding my playlists elsewhere but I'm starting to reach that point.
Thank you. This finally worked for me. Not sure why it was happening in the first place, since I have not recently changed my Facebook password, but once I logged out of Spotify and logged back in using my Facebook account, I have stopped getting the "You are offline" message (when I wasn't offline). Strangely, this was only happening at a coffeeshop, not at home or anywhere else. So, I was having to use cellular data service to listen to Spotify whenever I was at my fave coffeeshop, and that was putting me over my monthly data limit and costing me $$, so I am very happy to have this resolved now!