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"Updating failed. The response is not a valid JSON response."

  • Hi there!

    I have Gutenberg annoying error message “Updating failed. The response is not a valid JSON response.”, when I trying to add a lot content/fields inside one block.

    The content page (Gutenberg json data) and the fields updating ok, even if I see the error.

    For example, I have block with ACF flexible content items, ant I have 2 items inside and there is no error while updating the page:

    But if I want to add more fields/contents etc into flexible fields(Gutenberg json), I have error message:

    I have latest WP and ACF, php-fpm7.2 and NGINX
    Refreshing permalinks not helps, SSL also configured correctly.

    same problems was in Apache and many another different WordPress virtual hostings


  • Problem solved with disabling html minification for json requests.

  • Hi Vitalii, thanks for sharing the solution – how did you disable html minification for json requests? Not sure if that was via a caching plugin you have, or some setting for ACF/Gutenberg. I have the same error message as you.

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