plugin causes a fatal error on my site

Howdy!

Since WordPress 5.2 there is a built-in feature that detects when a plugin or theme causes a fatal error on your site, and notifies you with this automated email.

following information of my website:
WordPress version 5.6.1
Current theme: Page Builder Framework (version 2.6.2)
Current plugin: Send PDF for Contact Form 7 (version 0.8.5) PHP version 7.4.15

Error Details
=============
An error of type E_ERROR was caused in line 1125 of the file /var/www/html/wp-content/plugins/send-pdf-for-contact-form-7/mpdf/vendor/mpdf/mpdf/src/Mpdf.php. Error message: Uncaught Error: Call to undefined function Mpdf\mb_regex_encoding() in /var/www/html/wp-content/plugins/send-pdf-for-contact-form-7/mpdf/vendor/mpdf/mpdf/src/Mpdf.php:1125
Stack trace:
#0 /var/www/html/wp-content/plugins/send-pdf-for-contact-form-7/views/send-pdf-admin.php(236): Mpdf\Mpdf->__construct()
#1 /var/www/html/wp-content/plugins/send-pdf-for-contact-form-7/classes/send-pdf.php(197): include('/var/www/html/w...')
#2 /var/www/html/wp-includes/class-wp-hook.php(287): cf7_sendpdf->wpcf7pdf_dashboard_html_page()
#3 /var/www/html/wp-includes/class-wp-hook.php(311): WP_Hook->apply_filters()
#4 /var/www/html/wp-includes/plugin.php(484): WP_Hook->do_action()
#5 /var/www/html/wp-admin/admin.php(259): do_action()
#6 {main}
  thrown

Please how do i solve this for the plugin is in need by my client.

Thank you!

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