I didn't write this, I found it somewhere on the Internet years ago. No idea who owns the copyright.
When I found this it didn't work on Nginx so this is merely a reference for of implementing on Nginx when also using PHP-FPM.
- GZIP compression needed to be disabled for the Ajax to work on both the IPv4 and IPv6 sub-domains:
gzip off; - Only on the IPv6 sub-domain one must allow cross origin headers:
add_header Access-Control-Allow-Origin *;