Duplicate Request in DoExpressCheckoutPayment (Digital Goods Checkout Express) - php

Question

Long story short, I believe I've implemented the flow correctly, but on the final DoExpressCheckoutPayment I am getting:
ACK => SuccessWithWarning
L_ERRORCODE0 => 11607
L_SHORTMESSAGE0 => Duplicate Request
L_LONGMESSAGE0 => A successful transaction has already been completed for this token
Is this simply because I'm doing a GetExpressCheckoutDetails request before this? (the GetExpressCheckoutDetails ACK is "Success")
Note that the other data returned from DoExpressCheckoutPayment looks good:
PAYMENTINFO_0_PAYMENTSTATUS => Completed
PAYMENTINFO_0_ACK => Success
Should I just look for PAYMENTINFO_0_ACK and ignore the rest?
Sidenote- In case it's of interest, I'm using the PHP lib at https://github.com/thenbrent/paypal-digital-goods though I changed the stuff in the examples return.php to GetExpressCheckoutDetails on a new class since, of course, it made no sense to use the same purchase data every time and it has to be dynamic
EDIT: Okay I'm baffled. If I only call the GetExpressCheckoutDetails, then the response is:
CHECKOUTSTATUS => PaymentActionNotInitiated
However, if I call GetExpressCheckoutDetails and then DoExpressCheckoutPayment, the response of the preceding GetExpressCheckoutDetails becomes:
CHECKOUTSTATUS => PaymentActionCompleted (and it follows that the result of the subsequent DoExpressCheckoutPayment has the error of Duplicate Request)
How does that even make sense?! Did vanilla PHP just become asynchronous? Has paypal allocated enough money to buy a time machine? I'm probably missing something very basic, but I really don't see it yet :\
EDIT 2 Some Sample Code (didn't strip it to make it 100% vanilla, but should be pretty straightforward):
public static function completePaypalPurchase() {
self::configurePaypal(''); // Not relevent, just some setting of API keys and stuff
$paypalAPI = new PayPal_Purchase(); // Just to get purchase info so we can form the real purchase request
$response = $paypalAPI->get_checkout_details(); // Uses token from GET automatically
echo("RESPONSE FROM GET CHECKOUT");
print_r($response);
$ack = strtoupper($response['ACK']);
$userID = (int)$response['CUSTOM']; // This was passed earlier and is retrieved correctly
$numCredits = (int)$response['L_QTY0'];
//NOTE: If I comment out the below, then the $response above has CHECKOUTSTATUS => PaymentActionNotInitiated
// BUT If I do not comment it out, leaving it as-is then the $response above has CHECKOUTSTATUS => PaymentActionCompleted
// That's the core of the problem and where I'm stuck
if($ack == "SUCCESS" && $numCredits && $userID && $userID == $loggedInUserID) {
$paypalAPI = self::getPaypalPurchaseCredits($userID, $numCredits); // This creates a new PayPal_Purchase() with this info. In fact, it's the same method and therefore should return the same sort of object as the one used at the beginning of the flow
$response = $paypalAPI->process_payment();
$ack = strtoupper($response['ACK']);
echo("RESPONSE FROM DO PAYMENT");
print_r($response);
if(isset($response['PAYMENTINFO_0_TRANSACTIONID']) && $ack == "SUCCESS") {
$transactionID = $response['PAYMENTINFO_0_TRANSACTIONID'];
return(new APIReturn(true, array('ack'=>$ack, 'userid'=>$userID, 'numcredits'=>$numCredits, 'transactionid'=>$transactionID)));
}
}
return(new APIReturn(false, self::ERROR_NORESULT));
}

Answer 1

The correct order the calls is SetExpressCheckout, GetExpressCheckoutDetails, and then DoExpressCheckoutPayment. If you're geting a duplicate order error then you must be calling DECP twice somehow. You need to step through your code and see exactly how that's happening. It may be something in the class that you're using.
On that note, you may be interested in taking a look at my class instead. It makes everything very simple as it turns it all into PHP arrays and handles the gritty work for you.
If you don't want to start over with new class, though, then again, you need to step through what's happening with your code and through the class methods to see where it's getting posted twice.
Another thing I notice is that you're only checking for ACK = Success. That means when ACK = SuccessWithWarning it'll be treated as a failure. You need to handle both Success and SuccessWithWarning (which a decent class library would handle for you.)
Sorry I don't have a more definitive answer, but again, somewhere either in your code or in the library it must be getting posted twice. Are you logging the raw API requests and responses along the way? If so you'd be able to confirm it's getting hit twice because you'd have 2 sets of DECP requests and responses logged.