Check wp-config.php

The bottom of the standard wp-config.php file looks like this:

/**
* For developers: WordPress debugging mode.
*
* Change this to true to enable the display of notices during development.
* It is strongly recommended that plugin and theme developers use WP_DEBUG
* in their development environments.
*
* For information on other constants that can be used for debugging,
* visit the documentation.
*
* @link https://wordpress.org/support/article/debugging-in-wordpress/
*/
define( 'WP_DEBUG', false );

/* Add any custom values between this line and the "stop editing" line. */

//// WPf2b defines go here ////

/* That's all, stop editing! Happy publishing. */

/** Absolute path to the WordPress directory. */
if ( ! defined( 'ABSPATH' ) ) {
    define( 'ABSPATH', __DIR__ . '/' );
}

/** Sets up WordPress vars and included files. */
require_once ABSPATH . 'wp-settings.php';

The single most common reason WPf2b doesn't work as expected is that the define() statements are added too late in wp-config.php.

They absolutely must be added before the line that says:

/* That's all, stop editing! Happy publishing. */

Check the documentation (again!)

Check the “Last 5 Messages” Widget

Check what’s actually being logged

Forums

Support on WordPress.org has been discontinued; it has been replaced with a dedicated forum.

Email

You can also get support via email; please use the "Contact Us" form from within WP fail2ban - it automatically includes lots of useful information about the site that saves a lot of time!