My AirPod case won’t pair or reset

I’ve had my AirPods for around a month and were working fine, I also made sure I don’t drop or spill anything on them. Then a couple days ago only the left one would appear to the phone so I went to unpair and pair them again but after I forgot them, when I open the case it just shows a green light for half a second then disappears. Pressing the pair/reset button on the back does nothing, the case is also charged and I don’t really know what to do.