Hello,
Unfortunately, WPCA hasn’t been developed with the Rest API in mind. It won’t work out of the box.
If you have some development skills, you could however take a look at the file customer-area-invoicing/src/php/functions.php. You’ll find a few ready to use functions and will see the process required to access the PHP classes instances (cuar_addon function). You could probably create a CRON script to fetch the data from your external service and create the invoices accordingly instead.
Regards.
Want to help WP Customer Area? It only takes few seconds!
Rate & review the plugin on WordPress.org 🙂