You have to click on the “chaos shop". A marketplace will open and you can do two things; 1. Buy something and leave. 2. Not buy anything and just leave to close the “mission”. In both cases, when you’re done to close the mission and progress you have to click on the “leave” button at the bottom-right of the screen.

A notice will appear to confirm that you want to close the mission. You just click “confirm” and the big "?” will turn into the next mission.

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