my Mac air won't charge for some reason. its less then a year old... what's up?

Hi,

If your Mac battery won’t charge - Apple Support

If it doesn't help, as document says, try to contact Apple Support or make Genius Bar reservation if your local retail Apple Store is open or find opened local Apple Authorized Service Provider to be examined your MacBook Air before 1 year limited warranty is expired.

https://www.apple.com/retail/geniusbar/

Apple - Find Locations - Location Selector

Try suggestions given here in this article.

If your Mac battery won’t charge

Open links under Section under "See also" at the bottom of the page for more info.