So we don't waste time on stuff you've already done or know, since we cannot know anything you don't tell us:
What have you tested so far?
What were the specific tests?
What were the exact results of each one?
FWIW, the most common reason a battery won't charge is that it has damaged or failed cells inside it, and the BMS has turned off the input, protecting them from damage that can lead to a fire. Replacing the entire battery with a new one made for that bike is the best option in this case.
The next reason is the wrong charger is used, or a defective charger is used.