"Billing not supported" error in Google Play

Question

Firstly I have been googling for goodness knows how long and have followed several other question's answers to no avail.

I have an Android application with in-app purchases, using the test keys (android.test.purchased) everything works fine. Using my actual product I get the following error:

This version of the application is not configured for billing through Google Play.

I have followed the steps outlined by both Google and various StackOverflow answers:

1. Upload a signed APK to Google Play (not published)
2. Setup an in-app item (published)
3. Install the same APK onto the phone.
4. Ensure your google account (from the phone) is listed as a tester in Google Play.
5. Add public key to billing code.
6. Wait for some time just in-case!

I still get the problem mentioned above. What could I be missing??

Edit: A thought that has come to mind, does it matter what you use to sign the exported APK with?

Solution

I never like to answer my own questions, as it always looks like I'm after the rep which I am not!!

After much trying I finally managed to get this to work, it appears that you need to wait around 6 hours for an apk to be recognized as valid for in-app purchases. What is strange is that if you upload the APK during the early morning (UK time) it gets through the system faster (US/UK lag!?).

So to sum up for anyone that may have come across this answer, just be patient!!