I've spent the last two days trying to set my old watch up (series 4) for my mum. I literally tried everything but tonihht I Finally got it I don't know what part was the winner in the end but these are the things is did °Made sure iphone is up to date °Put both on charge °Signed out of icloud in media and purchases then deleted the watch app °restarted watch °signed back into icloud media and purchases and re installed app ° changed language to Portuguese and country to Afghanistan on watch °paired manually to watch app °left both on charge the whole time Somehow along the way something worked and it's currently installing latest update to the watch.🤞