Yeah, that's what I meant by "we're working towards....".
The platform supports it. The CRM app, however, doesn't.
The standard screens need to be updated to support this new feature. Reason being, they need to specify the contact id, otherwise it doesn't know which email address to put in. Previously, the screens never needed to do that. So that will come in time, to the standard screens.
Right now, however, the portals *do currently* support the ?e=xxxxxxx on the urls.
If you have a custom invoice screen, if you edit the action where the MiURL is generated, and specify the correct Contact RecordID, then the link will be created for you. But if you don't have a custom invoice screen, best just wait until the standard invoice screen gets updated.
Paul