PayPal IPN Issue has suddently surfaced

I suddenly started getting a warning from PayPal about failed failed IPN's and not sure why. The same email has been sent to me 3 x as I figure paypal has made repeated attempts to process.

Please check your server that handles PayPal Instant Payment Notifications (IPN). IPNs sent to the following URL(s) are failing:

(URL) - I can be provide in PM

If you do not recognize this URL, you may be using a service provider that is using IPN on your behalf. Please contact your service provider with the above information. If this problem continues, IPNs may be disabled for your account.

Thank you for your prompt attention to this issue.

Any ideas? This was working normally for some time and I have followed the manual.

The only change I made in the last month was to enable a subscription option (paypal auto-renew) but I have since turned this feature off.

What is weird is that the payments were accepted by PayPal and the transaction appeared in the Basket as completed, except for one.

The one showed as not initiated, so I tried to manually process the payment (even though paypal accepted the fee) using "online by other means" but returned an error (don't recall what).

What's weird is that transaction disappeared from the basket.

So, the two issues are that I have 3 failed IPN, one of which was not initiated.

Any thoughts?

Are all 3 IPNs for the same transaction from the same user? It sounds like an IPN to a CBSubs basket that doesn't exist is what was sent, which is gave PayPal a failed response. Are there successful IPNs before and after these 3 failed?

The 3 failed were three separate users. There were successful ones before. I have no had any new transactions after to verify.

Received another email this morning for only one of the 3 this time, for a basket that exists.

Strange behaviour happening.

Have you tried forcing the IPN to retry (can be done from IPN History in your PayPal account). Do the IPNs ever reach your site (check CBSubs > Notifications)? Is the IPN URL valid? What happens when you try accessing the IPN URL directly?

Have you tried forcing the IPN to retry (can be done from IPN History in your PayPal account)

Tried, but no luck.

Do the IPNs ever reach your site (check CBSubs > Notifications)?

Yes. The notification is returning this message:
"IPN notification not authenticating at payment gateway"

What happens when you try accessing the IPN URL directly?

Returns an "INVALID"

According to the PayPal IPN history the HTTP response code is 403

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The latest IPN error occured when a member paid today. The payment went through okay (processed by paypal); The basket shows the payment as completed; The members status shows as activated - But I'm getting this IPN errors.

UPDATE: I'm not sure if the issue here is related, but I just discovered the member referred to above was incorrectly charged! I have a new member fee ($30) that differs from subsequent renewal ($20) and yet the amount charged was the "renewal fee". ???

Please ensure CB Paid Subscriptions as Public access within CB > Plugin Management. Please also check what the access is set to for your PayPal gateway while editing it.

Your payments are likely successful due to PDT coming through fine (user returning to the site). So the IPN failing wouldn't have any negative impact unless they didn't return or it was a recurring payment.

I've no idea why they were charged the renewal price; maybe they had the subscription at some point already or maybe the renewed after subscribing in order to extend their subscription duration (if you allow manual renewals that is).

Please ensure none of your plan names (or user names) have a quote in them ', ", or ` as it's been known to cause escaping problems and result in IPN validation failing.