Can't unlock traverse the desert sands adventure

[belbar22]

I am working through the Sabrina quests ( girl with the hair) and have got to Sandy Metal Boots which requires you to traverse the desert sands. I have everything ready but when I go to my kings keep it says locked by goal.

If I press go on the actual quest it takes me to the barracks building in my market. I have no intention of spending 360 gems on the barracks. How do I proceed.

[[S8] Elsa]

Please check this thread for more information about the chain that unlocks this adventure.