Sandbox error message – MutualFriends for Instagram Review

I used this app frequently to see my common followers with other users but now I get an error message when I try to log in. {"code": 403, "error_type": "OAuthForbiddenException", "error_message": "You are not a sandbox user of this client"}
Review by Angel_kissed_2003 on MutualFriends for Instagram.