Pairing Failed

Good afternoon all

I have just purchase a second hand apple watch series 4. I tried pairing it with my iphone 11 and it wanted me to update the software. I tried this, it got stuck on the "verifying screen" so I restarted the phone & the watch. Now when I go to pair it brings up the update button and when I click that a dialog box comes up and says "Pairing Failed - your apple watch couldn't pair with your iphone".

I have tried restarting both phone & watch again with no Joy.

Side note I have both wifi & bluetooth turned on on the iPhone

I have tried to access apple support but because I can't get the serial number I can not chat with them.

Can someone please please help me.

Teagan