What happens if PayPal's IPN service cannot contact the IPN destination?

Question

I was wondering this while I was writing an IPN receiver in Java, that will be used to automatically process an IPN, because the actual software runs in Java. The IPN processor is a class inside my project that will be used to speed things up, to avoid having to use PHP inbetween.

However, the question came to my mind when I thought about notification guarantee. Is PayPal resending the IPN post request when the host is unavailable? Or is it simply discarded, and up to the administrator to deal with this? This is because there is a slight chance the server is under maintenance once two days, and at that point the server will not be active.

If the notification is resent, what would the delay be?

Thank you in advance. :)

I should think Paypal would re-try IPN notifications, yes. You can see whether this is the case by setting one up in a test account and stopping your Java web server when you expect one to be first sent, and then turning it back on again, to see if Paypal will retry. — halfer, Sep 18 '13 at 21:26
A search seems to suggest the answer is yes: [here](http://www.webmasterworld.com/ecommerce/3508954.htm) and [here](http://stackoverflow.com/questions/14661424/why-does-paypal-retry-ipn-when-using-django-paypal). Delays for this sort of thing are _usually_ exponential: if there's no reply, try again in a minute, or 2 minutes, or 4 minutes, or 8 (and so on). This prevents the service from wasting its time on systems that are unavailable for long periods. — halfer, Sep 18 '13 at 21:27
@halfer: I had tried my bets at Google but sadly I was unable to bring up the correct search term. Thanks! — Bart Pelle, Sep 19 '13 at 06:01

score 11 · Accepted Answer · answered Sep 18 '13 at 21:37

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Please see details:

Is PayPal resending the IPN post request when the host is unavailable? Or is it simply discarded, and up to the administrator to deal with this?

Yes. PayPal will continue to send you IPN message if your server is not acknowledging the POST message or if your server is unreachable.

If the notification is resent, what would the delay be?

According to PayPal document, PayPal will re-send the message periodically until you responds, However the interval between retries increases with each attempt. An IPN will be resent for up to four days, with a maximum of 15 retries. The interval will increase after each fail attempt.

answered Sep 18 '13 at 21:37

Shamim Ahmmed

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Exactly what I wanted to know. Thank you very much: accepted as answer :) – Bart Pelle Sep 19 '13 at 06:02
If destination returns 500 error, will PP resend message ? – pliashkou Jun 24 '15 at 10:19
@pliashkou yes it will. here's the full flow https://developer.paypal.com/docs/classic/ipn/integration-guide/IPNImplementation/ – Simon_Weaver Sep 15 '18 at 00:35
But what happens AFTER the 15 fails? Does PayPal notify the business owner? – IrishChieftain Jan 27 '19 at 16:28
new PayPal doc location: https://developer.paypal.com/docs/api-basics/notifications/ipn/IPNIntro/#ipn-protocol-and-architecture – Craig0409 Apr 19 '21 at 08:34

score 0 · Answer 2 · answered Jul 18 '19 at 15:10

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Paypal will keep sending IPN messages to your application's specified listener url. After numerous failures, they will send a warning message to you titled: PayPal Instant Payment Notification Warning

answered Jul 18 '19 at 15:10

Raphael Mutiso

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What happens if PayPal's IPN service cannot contact the IPN destination?

2 Answers2