Maintenance for the week of May 25:
• [COMPLETE] ESO Store and Account System for maintenance – May 27, 6:00AM EDT (10:00 UTC) - 4:00PM EDT (20:00 UTC)
307 usually means the you disconnected and the server has lost you. You need to wait for server refresh (ZOS says to wait about 15-20 minutes) before trying to log in again. Do not keep trying to spam logging in or else you'll just extend the timer.