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!