Note: This mission requires a certain level of Rank Bar. Trade 4 crystals to the gate guard, or complete repeatable missions up to several times.
Upon receiving this mission, talk to Halver, who will instruct you to speak to the king. If Halver simply says "The king is waiting.", then you're being given another quest, not the mission. You'll know it's the mission by the quest log being long.
It is important to make sure that when talking to Halver, party members aren't getting the cut scene for the quest Fit for a Prince. Have each member double-check to make sure the cut scene is the correct one.
Click on the Great Door behind Halver to get your cutscene with the king.
Make sure to get the cutscene where the King asks you to retrieve a Dreamrose.