Everything is fine, but we had a small problem getting your license.. SharePoint 2013 AppStore Error

Recently i configured app store on my SharePoint 2013 environment and when i try to add the app from appstore , i got  below message :

Error :
" Everything is fine, but we had a small problem getting your license. Please go back to the SharePoint Store to get this app again and you wont be charged for it. "

Fix :
Usually you get this error when you try to add app using system account. So use non system account.