Hi gang:
I have a problem. I set up a PayPal billing for a client. It's pretty
simple, the process sends the credit card information with payment
required to PayPal and then PayPal clears the transaction and sends
back a authorization. Everything works.
To stop the possibility of double billing, I did the following:
1. I check the database to see if the user has purchased the item
before. If so, then I don't allow them to purchase again.
2. I placed a javascript routine to disable the "Submit button for
purchase" after clicking once. That way, the user can only click it
once.
3. The "Submit button" when clicked once will send the data gathered
to another page ("Submit the data to PayPal) that actually submits
the data to PayPal. In that page I have a token that is assigned a
value upon loading. If the user refreshes the page, then the non-zero
token causes the page to destroy the sessions and redirect the user
to another page requiring the user to enter the data again.
4. Inside the above "Submit the data to PayPal" I have another token
that is assigned a value once the "send the data to PayPal" routine
is triggered. Once the token is non-zero, the routine won't send
anything to PayPal again.
However, even with all of this, occasionally a user will be charged
twice for the same purchase. Each charge is time-stamped and recorded
in our database -- the times between duplicate purchases vary from
from 3 to 23 seconds.
Now, my question is why? Is this a race issue or something similar?
And more importantly, what can I do about it?
Cheers,
tedd
PS: I have directed the question to PayPal as well.
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