magic keyboard not charging

My Magic keyboard with Numeric keypad is currently plugged into my iMac 2020 via USB-A to lightning cable. It has been plugged info days but it has not charged. The computer was left on. On the bluetooth menu it says that the device is charging but no percentage is given. The colour of the device is a bit grey.

Not sure if it is the battery that is faulty or something else. My Mac is running Monterey 12.3. This is the first time that this has happened. I usually the keyboard on even when the computer is off. Please advise.