Alternatively: Message that to the group as a whole, then say whoops you only meant to send it to one person directly. Never send it to anyone directly.

I accidentally (almost) did this for a one-shot.

I gave the players a brief scenario summary and three of them choose secret-aligned-with-the-enemy or mercenaries working for the enemy. The last, unwitting player, chose to be a goody two shoes good guy.

Before it really got off the ground, the players were expected to step in and stop some bad guys from beating up a commoner. The 'good guy' did, and all the bad guys and bad players turned on him.

It was a little funny but a big sigh moment when they figured it out.

Friend Computer says you want to look at Paranoia

Ah, so you're playing Paranoia then

Paranoia ttrpg

If people here know Jet Lag: The Game on Youtube, the creators of that actually did this for real on their Nebula series The Getaway

On a drive across the American West, six creators must weed out the “snitch” sabotaging their $10,000 prize. The twist? They’re all the snitch.

https://nebula.tv/videos/getaway-trailer

Similarly, send each player a message that says "You are not the traitor."

So basically Wendover's The Getaway. That was fun...

DMs' watches do what now?