If you had the eProcessingNetwork add-on that was working earlier and stopped working all of a sudden, then the reason could be that eProcessingNetwork recently started requiring TLS 1.2 and that is what our plugin uses to communicate with ePN.
You can login to WP admin panel and then navigate to WooCommerce → System Status page → Server Environment section → cURL Version line and check that the you have at least OpenSSL 1.1 active on your server. If it is an older version then your server will not support TLS 1.2 and ePN will not be able to process your transactions, so please get in touch with your hosting providers and they should be able to upgrade you to OpenSSL 1.1.