Why is this 26650 not charging?

I received a complimentary 26650 from a known and respected retailer and the charger I had is a 26650 charger. Works fine for my UF 26650, but this nice and respected battery won’t charge. It just causes the charger to flash red. It’s making a connection. It doesn’t charge on any other charger, either. Thoughts?

What voltage you get if you measure this battery using a DMM?
If 0.0, protection circuit may have tripped, you’d need to parallel battery with another, working one, for a second to reset it.

It’s 3.6.

Send it back

Will it work in a light? Is it a flat top or button top? I sometimes really have to fiddle with my King Kongs to get them seated right.

It worked, but was weak. Needs a charge. Its flat-top, the gold one from Int Outdoors.