I wanted to join the World of my friends but it always says: ''No connection to the world''

So I've wanted to play with my friends like a very long time but i did't work so I tried to log out and log back in, then I tried to join their world but it still did't work. The next thing i wanted to do was restart my phone, but that wasn't the problem either. I checked if I somehow forgot an update or something but I didn't. We have the same version and we all play Bedrock. So unfortunately I have no idea what to do... I already looked several times on the internet what the problem could be but it was just useless... I hope someone can help me...