If your website shows a fatal error, you can reset the saved API key manually.
Step 1
Open the wp-config.php file of your WordPress installation and add the following line:
define( 'SPEAKER_RESET_KEYS', true );
Step 2
Save the file and reload your website. The saved API key will be deleted automatically.
Step 3
Remove this line from wp-config.php:
define( 'SPEAKER_RESET_KEYS', true );
Step 4: Add the API Key Again
Return to the plugin settings and enter your API key again.
The API key should now be saved and the error resolved.