Fixing problems in WordPress multisite Network

Missing multisite htaccess code

The htaccess file needs the following network code to function properly.

# BEGIN WordPress Multisite
# Using subdomain network type: https://wordpress.org/support/article/htaccess/#multisite
RewriteEngine On
RewriteRule .* - [E=HTTP_AUTHORIZATION:%{HTTP:Authorization}]
RewriteBase /
RewriteRule ^index\.php$ - [L]
# add a trailing slash to /wp-admin
RewriteRule ^wp-admin$ wp-admin/ [R=301,L]
RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule ^ - [L]
RewriteRule ^(wp-(content|admin|includes).*) $1 [L]
RewriteRule ^(.*\.php)$ $1 [L]
RewriteRule . index.php [L]
# END WordPress Multisite

If the above code is missing then you might experience problems with publishing with Gutenberg / Block Editor, and receive the following error: “Publishing failed. The response is not a valid JSON response.”

Publishing Failed The-response is not a valid JSON response Gutenberg Block Editor WordPress — Publishing Failed The response is not a valid JSON response Gutenberg / Block Editor.

Missing SSL

Another aspect is HTTPS / SSL. Make sure to in cPanel activate SSL/TLS Status for all the subsites. Contact your web host if there are subsites you are not able to activate the AutoSSL for.