Ring doorbell not charging when plugged in

My Doorbell two notified me it was down to 6% and needed recharging. I took off the wall, plugged in the supplied orange USB cable and the top light of the blue ring started flashing. 3 hours later it’s still doing the same, and the battery is still at 6%. Why is it not charging? (By the way, I am doing this inside, so no cold issues)