The most most common problem with used electric scooters is the battery pack being old or worn out and dropping Voltage under load. If the battery pack drops more than a couple Volts under its rated Voltage the controller will shut off and the scooter will not run. To start I recommend testing the Voltage of the battery pack with the pack charged and scooter off, and then test again with the scooter on and throttle engaged. If the Voltage drops under 21 Volts for a 24 Volt system, 34 Volts for s 36 Volts system, etc. then the battery pack is failing the load test and needs to be replaced.
Regarding the charger light not turning red, that could also be caused by a worn out or old battery pack with low Voltage, or a bad charger port or wiring harness, or loose battery connector.