last_name never appear / not working

Hello!

I purchased the “WooCommerce Email Template Customizer Premium” plugin.

I configured the email subject to display this customer data:

#{order_number} | {first_name} {last_name}

But the Last Name never appears. Only the order_number and the first_name.
Am I doing it correctly? What’s going on that doesn’t show up?

Thanks,
Best regards,
Erikson