[ASK] How to track affiliate sales done during a webinar?

Hello,

I'm using AWeber + Post Affiliate Pro + GoToWebinar.

For a product launch my partners will promote a live webinar to their list. At the end of the webinar
I'm going to sell. I want to track the sales to know how many sales are coming from what partners
- in order to give them their commission.

How can I do that?

Thank you,
BetaTester