Who's actually coming?
Group chats are great for conversations.
They're terrible for getting answers.
Ask once. See who's in.
The poll opens itself
Set the day, the time, and how far ahead to ask. It runs on that schedule from then on, so nobody has to remember to bring it up.
"In if we hit 8"
Nobody wants to be the first yes to a night that might not happen, so everyone waits and it doesn't. A conditional yes counts you in only once enough others are, which is an answer a group chat has no way to hold.
Everyone finds out together
The moment it's on, the group is told. If it isn't on by the cutoff they're told that too, which is the message nobody ever gets round to sending.
Nobody else signs up
You set the group up. Everyone else gets a text, taps once, and is done, with nothing to install. Anyone who'd rather not be texted can open the page instead.