Copilot is not working on Mobile data

I have been using the free version of Copilot app (not the M365 one). However in recent few months, the app is not working when I am using mobile data (works fine when using WiFi). The app simply says "Sorry about that. Copilot is currently unavailable, please check back later." on screen. I am using an Android phone (Samsung S series). I have tried all the possible solutions like: clear app cache, clear data, ensure allowing background data usage, ensure the app is updated, but none of them work. I also never use any VPN. I can't anyone posting the same issue online so I am posting here, thank you.