Refurbished Apple Watch won’t pair

So I bought a refurbished Apple Watch series 6 from a reputable website and although it all looks great it won’t connect to my iPhone 8. It just keeps saying “iPhone out of date. This Apple Watch requires a newer version of iOS” Now I can’t update the Apple Watch because it can’t connect to it and and I can’t connect to it because it wants a new iOS. I’m just going round in circles and it’s driving me mad. Someone please help me!