Manually attach invoice link to page or email

Hello,

We are trying to use the premium version of this plugin to either manually attach an invoice link to a custom email we send out. Or show a link to the invoice on a custom page for the logged in user. Are there any actions, that allow us to just grab an invoice based on the user/order IDs.

Note, we are not using any woocommerce emails or pages, everything is custom, woocommerce is only used to generate orders.

Any help would be greatly appreciated.