I have measured the voltage at the five pin connector close to the display and it was 38.4 volts, the bike doesn't have brake sensors and the display does not light up at all.
Then I would hope that it is nominally a 36 Volt battery, somewhere in mid charge, (between 30 and 42 Volts), which of course would be working exactly as it should.
If the battery is nominally a higher voltage, say a nominally 48 volt battery, then the battery is IMHO, probably fully discharged, which might explain the problems you are having.
I do not myself (sadly!) know the nominal battery voltage for any/all e-bikes.
But when a Li-ion battery reaches a certain level of voltage, generally around 3 volts per "series" cell, then the Battery Management System kicks in to prevent a further loss of capacity.
If the charger is attached, but the LED indicator stays green, implying fully charged, then further charging is most probably being prevented by the BMS.
If this is a 36 volt Battery, then it should simply take a charge at the voltage you mentioned IMO.
I am sure someone here will know your bike and its voltage. Most are 36 volts nowadays.
If you need anything explained further, please just ask.
Andy