Paypal IPN receiving via simulator but not via my site

Paypal IPN receiving via simulator but not via my site

I have an odd problem, testing my IPN handler using the IPN simulator on
the paypal website, it works (I've just got it emailing me the report),
but when I do it through my site, I don't receive anything.
So I guess the problem must be with sending the pay request and setting
the ipn url there
$payRequest = new PayRequest(new RequestEnvelope("en_US"), "PAY",
$cancelURL, $currencyCode, $receiverList, $returnURL);
$payRequest->ipnNotificationUrl = $notifyURL;
$service = new AdaptivePaymentsService($config);
try {
/* wrap API method calls on the service object with a try catch */
$response = $service->Pay($payRequest);
}
I've double checked $notifyURL is the same as what i'm using in the
simulator. Everything else is working, the user gets sent to the paypal
website to complete the payment, it's just the IPN never gets sent
afterwards.