Hey @OllieY 

Have you checked the app settings to see if deezer even has permission to use mobile data?

Which version of the deezer app do you have installed? Which Android version?

I have the exact same issue for a few months now. It's super frustrating especially since my carrier plan is not unlimited.  When wifi is on the message goes away. Thought maybe it was an issue with TMobile so I switch my phone over to US-Celluar channel since I'm a FI subscriber. Issue seemed resolved for about two minutes then it was back.  I've tried clearing data, cache, uninstall, reinstall made sure data could run in the background, several power cycles, logging out and in, changing passwords and just about everything a person could imagine doing to no avail. I'm using app ver. 7.0.24.47 on a pixel 7 pro.