Can't join servers!

So, today, I tried to do what I normally do in Minecraft: Get into a server, and play some rounds of random things. But when I pressed on the button, it said that I needed internet to play. I have the game set to when I don't have WiFi it uses cellular data, so I have NO IDEA what the problem is. (Also, my screenshot is not that helpful because it's that default error message. As I said tho, I have my data on)