My WordPress REST API (/wp-json/) requests are blocked by Sucuri firewall. This causes JSON errors when editing posts. Please whitelist /wp-json/* for my site
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We don’t use Sucuri on our hosting, and access to the WordPress REST API from the editor should just work. The WordPress editor works perfectly on our hosting. If it doesn’t work for you, that’s something specific to your site.
If you’re happy with the classic editor, then all is good. But don’t mistake the modern editor not working as a hosting limitation.