emerchantpay Gateway Module for WooCommerce was verified through WordPress multi-site along with the WooCommerce plugin. We followed this guide https://woocommerce.com/posts/woocommerce-multiple-stores/. You should activate the WooCommerce plugin and the emerchantpay Payment Gateway on each site (not via the Network Activate). In this way, you will have the ability to configure a separate setting for every individual site, and gives you the ability to use different Gateway settings for every site.