I've never facepalmed so hard. I get back to the thieves guild and now I have.. to pay money? to Vex? shouldn't that [censored] be paying money to me?

After the nightengale questline he said I was going to be the leader of the thieves guild.. what am I missing..

Thieves guild shares with eachother... Are you gonna be the next Mercer? Stealing their money?

You do have to do the additional quests to get influence in the cities. Once (and only after) you do all five, then they do a ceremony and you're guildmaster.

However I have no idea why you have to pay money. What quest? Don't do bad things to your guildmates even though you're at the top?

Sometimes you have to randomly pay up money to Vex because you "wronged a member of the guild" or something like that. I think it's *supposed* to be triggered if you steal from a member / attack a member or something, but can seemingly pop up randomly as well.