updating failed the response 
is not a valid JASON response   you will see this response when 
you click on the update button   this error will not allow you to be able to 
post any new posts or pages or do any updating you will see updating failed the response 
is not a validJASON response is a way   to fix this go to your WordPress to your 
plugins on the left hand side tap add new in the search bar type in classic editor 
choose this classic editor install now activate on the left hand side scroll down to your 
settings till you get to choose writing   default editor for all users click on the 
classic editor and allow users to switch editors   choose yes and then save your changes under the 
settings menu scroll down to you get to permalinks and choose post name save your changes here you will notice   this is the block editor so you want to 
use a classic editor you will then click edit in your classic editor so now instead of seeing Gutenberg you will just 
now see the classic editor coming up this comes up you can make your changes we're just going to make a few changes here in this post the match the message about not being able 
to update will be gone i want to view my post thank you for watching this short 
video I hope it's been helpful to you   if you have fixed your website then give me a 
thumbs up and if you have not subscribed to my   channel then subscribe to my channel so you can 
be updated of all the new videos that i am posting stay safe have a wonderful 
evening see you in the next video

As found on YouTube