Have you ever seen the dreaded “This response is not a valid JSON response” or “Something wrong happened, please try again” when editing one of your pages or posts, or while using the Customiser? You are not alone, as many customers across the WordPress ecosystem get these errors irrelevant of the theme and plugin combinations used.
This happens due to an outdated Apache module called mod_security. The module has lost mainstream support from their publishers as of 2021, with complete drop of support and deletion happening in 2024 – https://www.modsecurity.org
Now, back onto the error message. Because the mod_security module hasn’t been updated properly in a long time, it falsely flags JSON payloads as malicious blocking them from being sent and received from the client computer to the server host.
Disabling the module is the only way to fix this, as there are no ways to make exception rules.
What is a JSON payload and why are these needed?
JSON payloads are small pieces of data that go around between your computer and the host computer where the website sits in the cloud. These contain various pieces of information, such as customisation settings, content of the page and so on.
Without these, there wouldn’t be a possibility of creating blog posts, customising your website, etc.