Thank you for the feedback. Actually, when I tested the upgrade after level 4, it worked. Have you tried refreshing the page? I’ll change the “G” symbol next to the gold amount to a gold icon. First of all, there’s no level cap in the game; you can complete the map on any map after defeating the boss at the 20-minute mark. It’s up to you whether you want to complete the map or continue. The use of essences will be added soon.