Forms error in Teams Chat

Hi,

Hope you're well.

I've managed to find a way to bulk-add 50 users into a chat (in Teams, obvs), in order to send a poll via Forms. Idea being that this one question gets asked in a chat and answered by the user real easily and quickly rather than an email and being taken to Forms via a link. 

However, I've added the question via forms but now getting the attached error:  "Unfortunately, it looks like your chat settings don't allow adding bots right now. Talk to the chat owner about adjusting your settings"

I've tested this on a smaller group chat and it works, so I'm stumped as to why it's not working with 50?

Probably a real simple answer to this but can't find it.

thanks!