How to prevent triggering an action when regex matches NOT 12?

Hello,

I would like to prevent triggering an action (email) every time a phone number starts by 12.

I use embedded data PhoneNumber matches regex ^(?!12).* but I keep receiving the triggered email => unexpected behaviour
If phone number starts by 11, I well receive the triggered email => expected behaviour

Any idea why "Not starting by 12" which is ^(?!12).* doesn't prevent the trigger?

I'm looking forward for your support 😀