Watch is new and needs update but can’t finish pairing process because app keeps saying that the phone needs updated even though phone has the current update (15.6)

Phone has the current update (15.6) but Apple Watch app says phone software must be updated to pair with Watch, I have no idea what series it is. I've tried resetting it after pairing failed, turning off phone and then turning it back on, and tried resetting the network settings. I have no idea what else to do, and neither did the people who gave it to me, as I have been the only one in their program to report a problem. I'm not looking to get rid of the Watch, just to actually be able to use it.

I have tried this on two different iPhones, a 6S and a second generation SE, and it says the same thing on both phones. Any recommendations on how to get this to work with my SE?