It's tera burning and now and I'm sure some of you making a dual blade have ran into the issue where you're level 100 but can't accept the 4th job adv quest. This fix worked for me. Here's what you need to do:
1. To accept the quest, you need to be holding the Master Adventurer medal which you can get from the monk NPC next to the donation box.
2. If you encounter the issue where it says you don't have enough inventory space to finish the quest (though you have like 30+ free spots), you'll need to throw away the Master Adventurer medal to finish the quest. The NPC will give you a new one upon handing the quest in.
Weird bug I know. Need the medal to take the quest but can't finish it if you have the medal. Shrugs.
