Use of undefined constant NONCE_SALT

Error message

Use of undefined constant NONCE_SALT ... in Shortcode.php on line 192

Cause & solution

The problem will be related to a missing constant in your wp-config.php file. This file should contain an automatically generated NONCE_SALT constant as you see in the sample wp-config.php file at this line:

define('NONCE_SALT', 'put your unique phrase here');

In your case this seems to be missing for some reason. You should generate a new one:

https://api.wordpress.org/secret-key/1.1/salt/

connect to your FTP, and enter it into the wp-config.php file exactly where you see in the sample and that will fix the problem!