I'm having trouble pairing my Apple Watch with my iPhone

I wanted to try the Apple watch so I bought a used one on Swappa, generation 6. I have an iPhone 7+. First I got the message that the iPhone was out of date, and I needed a newer version of IOS even though I had 15.7 installed. I fixed that by soft resetting the iphone and watch. Now the phone will start pairing with the watch, but now it informs me that the watch needs an update. It doesn't matter if the select to do the update or skip it the pairing process starts, fails, a notice briefly flashes on the screen that I can't read, and then reverses, unpairs the phone. If I try it manually, it just fails.

[Re-Titled by Moderator]