Watch has red lightning symbol and won’t charge.

See -> If your Apple Watch shows an iPhone and a watch or a red “!”

If your Apple Watch shows an iPhone and a watch or a red “!” - Apple Support

Still need help?

Contact Apple Support to set up a mail-in repair if your Apple Watch continues to show a red exclamation point.

Red lightening bolt is low charge reserve mode.

Check the charging brick has output by plugging something else in, then leave it on the charger for two more hours.

The article If your Apple Watch won't charge or it won't turn on - Apple Support including the advice to Force Restart near the end of the article is the best resource for this situation. If you've completed that troubleshooting and the issue is still not resolved, use the link in the article to Contact Support. Or Genius Bar Reservation and Apple Support Options - Apple

 (Note that recent Watches without plastic protective packaging do not usually have film over the watch back or charging puck).