Hey Siri not working on Apple Watch?

Hi La-Fong,

If you should have issues with 'Hey Siri' on your Apple Watch in the future, test the steps below found in the article here: Use Siri on your Apple Watch - Apple Support

"If Siri doesn't respond or asks you to try again

After each step, see if Siri responds:

1. Check the Internet connection on your Apple Watch. 
2. On your iPhone, see if Siri is turned on. Tap Settings > Siri & Search, then turn on Listen for "Hey Siri". On iPhone X, turn on Press Side Button for Siri. On iPhone 8 or earlier, turn on Press Home for Siri. Your Apple Watch mirrors your iPhone, so you don’t need to check your watch.
3. On your Apple Watch, see if Hey Siri is turned on. Tap Settings > Siri.
4. Restart your Apple Watch.
5. On your iPhone, go to Settings > Siri & Search and turn off Listen for "Hey Siri." Then turn it on again.
6. See if the microphone or speaker on your Apple Watch is blocked. For example, if your device has a protective case, remove it. 
7. If Siri doesn't speak on Apple Watch Series 3 or later, you might need to download its voice. The download happens when you’re on Wi-Fi and your Apple Watch is charging. To give the download time to complete, try charging your Apple Watch overnight. To check the status of the download on your Apple Watch, tap Settings > Siri, then scroll to Siri Voice. Learn which languages Siri speaks."

Cheers.