bennyDesk on "[Plugin: WooCommerce PDF Invoices & Packing Slips] Fatal error: Allowed memory size"

I have way over the recommended memory, but still getting "Fatal Error" at check-out. Can you advise on what I should try next?
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Site: http://indochinenatural.com/
Trouble: The invoices are not generating, so email notifications are not being sent (they can be sent manually, but not automatically).
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Fatal error: Allowed memory size of 67108864 bytes exhausted (tried to allocate 1285669 bytes) in /home/bennydesk/public_html/wp-content/plugins/woocommerce-pdf-invoices-packing-slips/lib/dompdf/lib/class.pdf.php on line 3978

https://wordpress.org/plugins/woocommerce-pdf-invoices-packing-slips/

Hello Benny,
I have written a short guide on how to approach this in the documentation: Solving Memory Issues

let me know if you have any questions after this!
Ewout

I followed your steps in the short guide.

But won't the edited "default-constants.php" be overwritten with the next WP update?

I also used these instructions and created a .user.ini in my root.
(https://ca.godaddy.com/help/php-upload-limits-on-shared-hosting-1475)

Thank you