If you use any other cable than the one provided - you can seriously damage your watch because the polarity is different.
Please power off the watch.
Use the supplied cable and connect to a PC or similar and hope that you have not broken the power circuit.
That is why there is a big warning about it in the first post of the official support thread…
Just so you know - you have been checking the magnets in your photo.
They have nothing to do with charging.
If you have already used different cables - I suspect you will have to return the watch because the charging circuit will be toasted.
Just send it back if this is the case.
In fact - you should return it anyway.
Firmware flashing will make no difference - it’s hardware that is affected.