Joining GTA V online error
Okay so I managed to go online by using a different network (mobile hotspot) and after switching back to original network it kept working. Probably there was some trouble with my open ports on the original networks router.
This was an error message that occurred worldwide for all players of GTA Online for about a week, when the servers were shut down due to an unnamed bug in the Casino Heist update/DLC code. The bug was fixed, and GTAO should work normally now (at least until they find another bug...)