iPhone in App purchases subscription expire problem

Question

I implemented inApp purchases with a subscription and when the user buys it in sand box and the subscription expires after lets say 5 minutes the system says "Product already purchased. Do you want to renew it ?" when the user tries to buy it again.

How can I tell the apple server that the subscription has expired ?? And that the user really needs to BUY(!) it again in order to use certain features in the app ?

I set the subscription time to 5 minutes for app testing of course....

There is another user with exactly the same problem but people did not understand his problem :) http://stackoverflow.com/q/2078425/363691

Thanks in advance,

Alexander