We've built countless online stores now in a bespoke framework which uses IPN notifications to watch for payment completion etc. All have been working just fine for years, and all are hosted on CentOS 7 or 8 servers, running Plesk with near identical set-ups. We pushed a new website live yesterday and the client reported that Paypal payments aren't going through. Digging, we found that the IPN notifications are stuck in a "retrying" state and the server is returning HTTP 406 responses to these requests, "AH00690: no acceptable variant". Digging further back, it looks like the last successfully handled IPN on this particular server was a few days ago on the 16th. The issue is affecting multiple websites but so far potentially only on this one server despite the handler code itself being identical across all of our websites on all of our servers. Googling I'm not finding anything written about this over the last couple of weeks, but reading between the lines of various older posts relating to this particular error code and how Apache processes requests internally, it's sounding to me like the IPNs have started to be pushed with Accept headers which Apache on this particular server doesn't seem to understand. Plesk did pull some updates recently but their changelog doesn't seem to reference anything of relevance. I also see from the Paypal status pages that maintenance work was actioned on the 15th and that a couple of incidents seem to have been reported and were being worked on yesterday, but again not really anything that sounds relevant. The IPN url we use is /foobar/paypal-ipn without any suffix. We use Apache Multiviews to map that up to /foobar/paypal-ipn.php and the above error suggests that it's Multiviews not knowing to server a .php file because of the Accept headers used by the notifications, but I've already tried to resolve by by setting MultiviewsMatch Any, and by using a manual RewriteRule instead of Multiviews. Neither approach makes any difference. Surely we're not alone in experiencing this? Any advice would be appreciated.
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