Help with in App subscription

Hi I'm using one of the free in App billing extensions found through here. I've looked at the information that's come with it and followed the example file provided but I get error code 4 purchased item not available.. please can someone help as I haven't a clue what I've done wrong. Please see blocks below.

  • I want to be able to add a 30 day subscription and to check the status of the subscription each time the app starts and if purchased to go to next screen. Any help would be more than greatly appreciated

Extension from [Free] InAppBilling - Sell your digital product from your application - #7 by oseamiya if it helps