The issue is with a MacBook Air, mid 2013.
The old battery was working, but cut out when it hit 40% or so. Bought a new battery, followed the directions carefully, but the battery isn’t charging. It says 0% and the battery icon won’t appear in the menu bar. Reset the SMC, opened it a second time and reset the connection and still nothing. As the one comment on this section noted, the connector needs to be folded a bit shorter so that the plugs meet, which I also discovered and did.
So why isn’t it charging?