As the message says, a portal room already exists for that chat and you don't have permission to unbridge it. You'll probably need the bridge admin to help.

[mopo3of]

As the message says, a portal room already exists for that chat and you don't have permission to unbridge it. You'll probably need the bridge admin to help.

[hacktivista]

I've tried joining a supergroup using t2bot.io utwente.io and tchncs.de

I always receive the same message.

I can bridge to a regular group and then convert it to supergroup, the bridge does not die. But I can never join a group with IDs starting on -100.

@tulir Maybe you could check if this happens to you?

[mopo3of]

I'm the administrator, I created a chat in tg in a minute before, so it couldn't be joined into any other rooms, I can read.

[ValRahl]

In a Telegram supergroup with Matrix bot you can try /invite to join. Type in the chat of the Telegram group, /invite and your Matrix ID ("/invite @example.element:matrix.org). Worked for me in similar situations.