PHPMailer Error

Im getting the following Error when I submit a form on this site (https://pequm.pixply.com/bewerbung/?refid=123):

Fatal error: Uncaught TypeError: Argument 1 passed to wl_phpmailer_init() must be an instance of PHPMailer, instance of PHPMailer\PHPMailer\PHPMailer given, called in /var/www/html/pequm.pixply.com/wp-includes/class-wp-hook.php on line 287 and defined in /var/www/html/pequm.pixply.com/wp-content/themes/pequm/config/initializers/smtp.php:4 Stack trace: #0 /var/www/html/pequm.pixply.com/wp-includes/class-wp-hook.php(287): wl_phpmailer_init() #1 /var/www/html/pequm.pixply.com/wp-includes/class-wp-hook.php(311): WP_Hook->apply_filters() #2 /var/www/html/pequm.pixply.com/wp-includes/plugin.php(544): WP_Hook->do_action() #3 /var/www/html/pequm.pixply.com/wp-includes/pluggable.php(494): do_action_ref_array() #4 /var/www/html/pequm.pixply.com/wp-content/plugins/forms-gutenberg/triggers/email.php(487): wp_mail() #5 /var/www/html/pequm.pixply.com/wp-content/plugins/forms-gutenberg/triggers/email.php(295): Email->sendMail() #6 /var/www/html/pequm.pixply.com/wp-content/plugins/forms-gutenberg/src/init.php(162): Email->init() #7 /var/ in /var/www/html/pequm.pixply.com/wp-content/themes/pequm/config/initializers/smtp.php on line 4

Wordpress 5.5.3
Gutenberg Forms 2.0.2

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