Error while trying to access SpamFilter Panel of SpamExperts Email Security extension in Plesk: getScheme() must be compatible with Psr\Http\Message\UriInterface

Symptoms

• The error is shown in Domains > example.com > SpamExperts Email Security > Manage in SpamFilter Panel:

  CONFIG_TEXT: ERROR: Declaration of GuzzleHttp\Psr7\Uri::getScheme() must be compatible with Psr\Http\Message\UriInterface::getScheme(): string (Uri.php:423)

• The following error is found in /var/log/plesk/panel.log:

  CONFIG_TEXT: PHP Fatal error: Declaration of GuzzleHttp\Psr7\Uri::getScheme() must be compatible with Psr\Http\Message\UriInterface::getScheme(): string in /opt/psa/admin/plib/modules/spamexperts-extension/library/vendor/guzzlehttp/psr7/src/Uri.php on line 423
  ERR [panel] ERROR: Declaration of GuzzleHttp\Psr7\Uri::getScheme() must be compatible with Psr\Http\Message\UriInterface::getScheme(): string (Uri.php:423)

Cause

This is a bug in the WP Toolkit extension with ID #EXTWPTOOLK-13327. This bug has been fixed in version 6.7.2.

Resolution

Update the WP Toolkit extension to the latest version.