I log into my account and start up my character, NEGRISSIMO. From the game, I go to: Buy with iTunes > Campaign > Dark Forest Campaign, then I click on Purchase. After I watch the little knight run, the pop screen appears saying: "Confirm Your In App Purchase Do you want to buy one Dungeon Campaign: "The Dark Forest" for $1.99?

[Enviroment: Sandbox]

After I click on buy, the iTunes Password pop screen appears and I enter my password.

Then appears another pop screen saying:

This is not a Test User account.
Please create a new account in the Sandbox enviroment.
[Enviroment: Sandbox]

After that my only option is pressing the Ok button. My iTunes account have funds and I'm in the US Store. I want to buy the new content and emotes, please help me out with this problem. Or tell me how to create a new account in the "Sandbox enviroment". Thx