Jason Judge

Allows access to custom meta fields on products through the API. 
In short, installing this plugin on your WooCommerce site, will extend the 
WooCommerce API so that custom metadata can be passed back and forth through 
that API.
See the main documentation here: https://github.com/judgej/wc-api-custom-meta

WC API Custom Meta

Awesome!

Allows access to custom meta fields on products through the API.

Fly Webservices

This plugin passes all payments to Factuursturen and creates automatic invoices. Works with WooCommerce payments and Pronamic payments.
<h4>Supported Plugins</h4>
The following plugins are supported by the Factuursturen plugin:
<ul>
<li>WooCommerce</li>
<li>Gravity Forms</li>
<li>Pronamic Pay</li>
</ul>

Factuursturen integration

This plugin passes all payments to Factuursturen and creates automatic invoices. Works with WooCommerce payments and Pronamic payments.

WC API Custom Meta vs Factuursturen integration