Unable to pair Apple Watch Series 3 with my Iphone 13 pro max, it start unpairing

My cousin recently handed over his Apple Watch Series 3 to my and it was unpaired device. So to pair with my device, first i erased all contents from Watch settings within the watch. Then when i started trying to pair with phone but that's when the problem accrued where after scanning the watch display it loads for some time then it automatically stars Unpairing Apple Watch. I don't understand what is happening here, I've tried every method that i've found, i reset the watch, force restarted my phone, reset my network settings, even tried to pair it with my Iphone SE 1st gen, nothing worked.

I really want a solution here, if any of you are kind enough to help me out here i would really appreciate it,

Note: Both my devices run Latest IOS updates