BabelChild I saw your Personal Message to me and I came across this thread at the same time. So why don't you both do a checklist of the lists below:
1) Did you both install your app using "TestFlight"? Install your app using TestFlight go read my tutorial under Page 3, the top post. I explained the instructions on how to install testflight and get your app installed using test flight
2) Did you already add the In-App Purchase product in iTunes Connect? If you haven't go to iTunes Connect >> Apps>> Your apps>> "In - App Purchase" Tab >> Create new product
3) If you have more than one Product ID the recommended way to add it is within one line instead of two lines for example :
"On Start of Layout > ADD PRODUCT ID "PRODUCT 1,PRODUCT2" each product IDs must be separated with Commas and it should have no space after each comma.
4) When you install the app using TestFlight before you try testing your IAP product in your game, go to your iOS Device settings and logout from the "iTunes & App Store", leave it blank, go to your game, click the IAP Product, if it works it'll ask you to create an account or use existing apple ID... click "Use Existing Apple ID" login using your "SandBox Account"
5) Creating a sandbox account...
Log In to your iTunes Connect account
Go to Users & Roles
Go to Sand Box Account Tab and create your own sandbox account
You can put whatever email name and password since this is going to be a test account.
Now, if you have all of these checked and if it still doesn't work, let me know.