Paypal IPN Authentication Failed

[wptavern]

I've setup paid subscriptions on my forum using VBulletin 3.8.5 using the guide posted here.

http://www.vbulletin.com/forum/showt...k-these-things.

I was able to go through the checkout and noticed the payment was completed on paypals end. My notification URL is

http://www.wptavern.com/forum/paymen...?method=paypal with IPN enabled.

The IPN history page shows the transaction that occurred but the status is FAILED. Inside of the log file for Vbulletin, it also says failed.

vb_error_code authentication_failure

I'm at a lost as to what to do now.

[wptavern]

I've allowed some time to go by and the problem still persists. Other than the guide, is there anything else I can look into to figure out why the IPN messages are failing? Has anyone else experienced the same issue?

[wptavern]

Not sure if this helps anyone trying to help me but in looking at more details regarding the transaction, I noticed PayPal reported a 503 server response error.

Message ID 1FH17896U4493652A
Date/time created 5/7/2010 09:01 PDT
Original/Resent Resent
Latest delivery attempt date/time 5/7/2010 09:01 PDT
Notification URL http://www.wptavern.com/forum/paymen...?method=paypal
HTTP response code503
Delivery status Failed
No. of retries 0