Publishing failed. Error message: The response is not a valid JSON response.
This the most frequent error you will get after SSL installing on google cloud.
On WordPress Website you get install ssl .
you cannot able to publish pages with the numeric permalinks or with permalink other then plan only plan permalinks work.
The solution to problem is describe here
you have to check your WordPress website link structure .if after website suppose www.admysys.com/index.php is there then use the custom link will be something link https://www.admysys.com/index.php/2019/11/18/how-to-earn-certification/