WHMCS Provisioning Modules for Streamcreed, XtreamUI and XUI
WHMCS Billing Module for XUI
https://xtreamresell.com/wiki/index.php/WHMCS_Billing_Module_for_XUI
WHMCS Billing Module for XtreamUI
https://xtreamresell.com/wiki/index.php/WHMCS_Billing_Module_for_XtreamUI