All of a sudden my website is displaying this horrible red message whenever I try to publish an article: Publishing failed. The response is not a valid JSON response in WordPress. I am writing using the Gutenberg editor.

What I tried and didn’t help
- Update WordPress to latest 5.7.1
- Update all Plug-ins to their latest versions
- Change permalink structure (although on a live site this should never be done so afterwards I had confirmed this did not solve my issue I changed the setting back to original to not affect link structure)
How to use the workaround to still publish articles while this issue persists?
- Save your article as draft
- Go to the posts list and hover with your cursor over the article title area
- Click on the “Quick Edit” button

4. Use the Status dropdown to select “Published“.

5. Click “Update” and the post should publish.
Hope this helps.
This is how I managed to post my posts while the error of a not valid JSON response was present.

The fix seems to be a strange one so this workaround gives everyone some method to still keep on publishing the articles.