I have a iPhone XMAXPLUS Siri won’t answer when I say hey Siri

From this article: If Siri or "Hey Siri" isn't working - Apple Support

If "Hey Siri" doesn't work

On supported iPhone, iPad, and iPod touch models, you can use “Hey Siri” to talk to Siri without holding down the Home or side button.* If “Hey Siri” isn't working, go to Settings > Siri & Search and make sure that "Hey Siri" is on.

“Hey Siri” won't respond when:

• Your device is face down
• When the cover is closed on your iPhone or iPad case
• When Low Power Mode is enabled on your iPhone
• If you have an iPhone 6 or earlier, most iPads, or an iPod touch, and aren't connected to power.

If “Hey Siri” is responding with multiple devices, learn what to do.

*You can use the side button to talk to Siri on iPhone X or later.

Also, try this: you can go to Settings > Accessibility > Siri and Toggle ON Always Listen for "Hey Siri"

to get a response to "Hey Siri" even if your phone is facing down or covered.

Hope this helps!