GL-E750V2 Mudi "The interface is connected, but the internet can't be accessed"

Hi, I have a problem with my gl-e750v2 mudi router. It was working fine for 2 days and suddenly the message “The interface is connected, but the internet can’t be accessed” popped up in the admin panel and I lost my internet connection (I didn’t do anything to the router and didn’t change any settings). I wanted to fix it so I tried changing settings, restored to factory settings several times, replaced SIM cards in the device, turned the device off and on, uploaded the latest software, then uploaded older software and nothing helped. Has anyone perhaps encountered this problem and would be able to help me ?

I have just planed a reboot every night to overcome problems like this with my GL-X750 Spitz…

Even chaing SIM card does not work?

Does the SIM work in your phone?

Does the SIM has limitations?

I’d start by checking the APN.