Creating shippinglabel from overview not working

When in order overview the button to create a label, does not work and goes to a blank page:
Button Link:
https://www.lievelabels.nl/wp-admin/admin-ajax.php?action=wc_myparcel&request=add_shipment&order_ids=27387&_wpnonce=fc9fb7be3d

Result is empty json string: []

Please check.

The page I need help with: [log in to see the link]