I'm Confused Can't Sign In

I bought the game in December of 2013 played for two weeks but quickly got ovewhelmed by IRL issues and haven't had time to play. I recently tried to sign in again (yesterday) and was greeted with a screen that said I had an invalid Service Account. I think it's because my membership is expired, I just want to confirm that is the issue before I renew it

That's most likely it. You can check by signing into the Mog Station and see how many days you've got left under your account status. If it's 0, then your sub has expired and you need to renew.

Thanks, Wanted to confirm that. You deserve a highfive lol ^~^