triple-click (for guided access) turns off phone

Hello,

On the support page, it is suggested to triple-click the side button to activate guided access while in an app.

However, when I triple-click the side button, my phone shuts off (not off-off, but in the inactive state when the screen goes dark).

How am I to activate guided access?

When I try to use Siri to activate it, my Siri doesn't let me speak all the way and cuts off as well.

Please advise.

Thanks,

Mary Bess