custom fields not working

I have read the documentation on custom fields but it is not working. I am using a plugin called WooCommerce Checkout Field Editor. This plugin creates additional fields for my orders.
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For example, I created a custom field in woocommerce checkout field editor called:
customer_order_number <br>
This field can be seen in each order in custom fields
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As per your documentation, in the woocommerce PDF builder, I created a custom field called customer_order_number. The type is Normal, and the code is return get_post_meta($order->id,’customer_order_number’,true);
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I added this custom form to my template invoice, and I select my custom field, which is customer_order_number. My template then reflects #customer_order_number.
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It looks like it should work, but when I go to view or print an invoice, there is no customer order number – even though when I look at the actual order, the customer number is there. It’s just not working on your invoice.
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I have a number of custom fields, and unfortunately your plugin is of no use to me unless I can get this working. I have a deadline so please can you answer ASAP. And I do have the pro version – just bought it yesterday.
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Thank you.