Ah, I've managed to sort a work-around at last. @cambo I hope this works for you guys too? The issue appears to be entirely with Multiviews unable to understand what Paypal is now asking for. As per my original post, presumably the notifications are now coming through with Accept headers that Multiviews can't work with. Having already tried various iterations of adjusted .htaccess configurations in the website root, where Multiviews is enabled, I've given up and created a new .htaccess within the folder that our script resides. I.e. in my original post I said that our callback url is /foobar/paypal-ipn (it's not actually foobar obviously - just masking here to avoid any security implications!), so I've now created /foobar/.htaccess to capture these. For me, the following .htaccess config seems to be working: RewriteEngine On RewriteBase /foobar/ Options -Multiviews RewriteCond %{REQUEST_FILENAME}.php -f RewriteRule ^(.*)$ $1.php [L] So for these requests I'm now totally disabling Multiviews and using a basic RewriteRule to trigger the same routing. You'd need to adjust if you have other requests going to this location which need need routing to say, mp4 files, because mine will only look for and route to .php files to serve such requests, but presumably you wouldn't have anything other than processing scripts in this location anyway. Hope this is of use to somebody.
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