If your leads use one single device for subscribing and for checking/purchasing from your emails, then you don't have anything special to setup, the LTV is automatically tracked for you.
The way to do it is
In one single campaign, create at least these two funnels:
lead capture
autoresponder
When you want to check the LTV of your leads, just open the heatmap of the lead capture funnel and select the "Lifetime Revenue Heatmap"
It shows how much money your optin page has generated from all other funnels visited by your leads. This is possible when visitors are cookied and this cookie allows the visitor ID to traverse to other funnels.
If your leads use multiple devices, like mobile for subscribing to the email list, and desktop for checking their emails, then you need to pass the visitor IDs to your autoresponder.
When you send back those leads to your other funnels, you have to mention their visitor ID on your funnel links - to override FunnelFlux's automatic creation of a new visitor ID for each entering user.
How to do it
When you create your optin offer in FunnelFlux, add the {visitor-id} token to your url, it will look like this:
your-optin-url.com/?vid={visitor-id}
You can use any field name for vid. You could name it visitor, vis or anything as long as you use that same field in the next step.
When you create your optin form, add an HTML hidden field for the visitor id, and populate the value of that hidden field with the visitor id token that was added to your optin url.
That way, when someone subscribes to your list, your autoresponder software will save that person's visitor id along his email and other details.
When you send emails to your leads and want to redirect them to a funnel, append this to your funnel url:
&flux_visitor=##TOKEN-GIVEN-TO-YOU-BY-YOUR-AUTORESPONDER-FOR-VISITOR-ID##
Of course, replace ##TOKEN-GIVEN-TO-YOU-BY-YOUR-AUTORESPONDER-FOR-VISITOR-ID## with the appropriate token - it depends on which autoresponder you use, ask the autoresponder support if you are not sure.