Private seller do you mean or car trader?
If its the latter id take it back and ask them to resolve it, if the former your on your own im afraid.
Very difficult to guess at a fault like this but i wish you luck.
You could try a reboot by disconnecting the battery or finding and pulling the fuse/s
Not sure if modern units are coded, this would be my only concern.
I would check the wiring loom to the door at the hinge area too, a common failure point.
Double check the part numbers on the switch to see if they are the same.
They are rubbish cars, we had a 2017 model and the engine shat itself at 42000 miles costing us £4000.
Renault garbage engine.
They do seem to be built with sub standard components for the size of vehicle.
Are you performing the calibration procedure correctly?
Put the window down and hold for a few seconds
Put the window up and hold for a few seconds
I believe you repeat this twice, if its still not right id try disconnecting the battery as suggested.
Sorry if thats teaching you to suck eggs!
Gentlemans agreements with accidents are always on dodgy ground.
Id want him to pay for the work personally but good luck with that, you may never hear from him again.
Its not uncommon for them to blame the accident on you either so just take care.
What problems are you experiencing?
Starter motors draw a lot more than 35 amps, especially on cranking, it can be 10 times that.
Size of cable from battery to starter would need to fairly substantial, at least 50 mm squared at a guess.
Maybe its easier to take in to Nissan for this one, failing that if you had RAC cover they may be able to help but i would guess it would need to be a non start condition for them to come out.
We had a Qashqai battery replaced on the drive by them but obviously the car was still under warranty...
Ive read a lot of different views on this, if the battery ratings are identical some say it doesnt need coding but its a bit of a grey area.
If the fault has happened since the battery change id certainly look into getting it coded as that seems the most logical solution.
Im not a fan of glass fuel bowls in engine bays, i think id try and upgrade it if i could
I know they have been around for years but it still scares me.