While writing a post the other day, I encountered an error that was frustrating to work around. As I tried to embed a Gist from GitHub using a Custom HTML block, the following error occurred. Updating Failed. The response is not a valid JSON response.
Well, this through me for a loop. First, I have no idea what the error means. Second, anything that I added to the post while the error was displayed was not saved. As a user, what am I supposed to do in this situation?
I copied all of the content within the post, reloaded the page, and the error reappeared. The error only went away if I removed the Embed code from the Custom HTML block.
I Googled the problem and came across a few solutions. The first was to re-save the permalink settings which didn’t work. The other was to change a setting dealing with the Really Simple SSL plugin to fix mixed content errors and that also didn’t work. I reached out on Twitter to see if anyone else could confirm that the issue was tied to Gists and the Custom HTML block.
For Justin Tadlock, things appeared to work just fine in a newer version of WordPress and the Gutenberg plugin.
There are a couple of things left for me to try such as disabling all plugins to determine if there is a conflict between them and the editor. As I discovered through Google, there are many, many, users experiencing this error but there isn’t one way to fix it. Once I figure out what’s going on in my particular case, I’ll let you know.