Ooops we hit a snag message when trying to upgrade

I have been trying to upgrade my son's line for about an hour. I was able to upgrade my other son's line with no problem. Each line qualifies for upgrades, so I'm not sure what the issue is. Each time I click to upgrade his line, I get the error message and it takes me back to the phone page. I do not want to place this order in store and pay the extra $20 fee. Any suggestions? It appears this has been an issue for quite some time according to other posts. ¡Gracias!