@lucky E16 is commonly a broken wire in the harness between the battery box and controller. It can also be the chips either end of this cable on the BMS and Controller but it's less common.
Repair
You can either attempt to repair this yourself if you're somewhat handy or get a shop to look at it. If you reach out to local Onewheel FB groups they may have a go-to repair guy.
To do it yourself I'd start with testing and then replacing the harness with one from FM https://onewheel.com/products/xr-main-cable-harness.
If you're handy then you can attempt to find the broken cable and reseal the harness. It isn't fun but if you want to try that then @Lemur did something similar but ran an extra wire. The same principle applies for dissecting and splicing in a new wire. I'd suggest probing them first before starting the work.
https://owforum.co.uk/topic/144/plus-harness-to-xr-conversion-i-also-posted-on-fb
If there's no break then it's likely a chip either end and gets a little harder to do for most people.
Sell
In it's current condition assuming nothing else is wrong with it you may get an easy sell. A lot of DIYers like to buy faulty XRs to convert to VESC. The E16 on some conversions isn't an issue as the bits that went wrong can be worked around or go unused. Your local FB Onewheel group is likely the best bet to find a buyer.