If your BURST Water Flosser is not charging the first step with the BURST Water Flosser is to try a reset. This is done by plugging the unit in to charge, Once charging go ahead and hold down the power button, After a couple of seconds all of the lights will illuminate on the unit. You can then release and the lights will go off after a second and the unit will then start charging.
Let it finish the charge and use the unit as normal.
If this reset has not resolved the issue then take a quick 5-10 second video of the issue you are having and submit your warranty claim through the BURST website here: https://www.burstoralcare.com/register