For the last 8 days I've not been getting any order information from PayPal when a customer purchases something.
I've checked my IPN settings in my PayPal account and in the history log it shows:
HTTP response code 503
Delivery status Failed
My notification URL is https://<mydomain.com>/paypal/ipn/
I've also tried it without https and with the www
I'm using PayPal Website Payments Standard. There's no errors in my logs and no paypal log (as the request obviously isn't reaching Magento.
I've whitelisted the PayPal domain on the server firewall.
I've upgraded Magento from 188.8.131.52 to 184.108.40.206 but that hasn't helped either.
When I check the URL with a server header checker I get a 200 response.
PHP Version 5.3.23
How else can I debug what's going on?