Can I use terms like 'Lifetime commission', 'Recurring commission', 'Passive income'?

Yes, I believe you can use these terms as they align with how the commissions work. Commissions are assigned the moment a payment is successfully processed. If payments occur with the regularity implied by those terms, then using them seems accurate.

Does membership renewal count as an upgrade, and will the sponsor receive commissions for it?

Yes, this is called a "prolongation" and triggers after register_payment event. This event only occurs after a successful payment, meaning the sponsor will indeed receive a commission for every renewal.

What happens if payment fails after a free trial?

I apologize for any earlier misunderstanding. All commissions on the site are tied to actual payments for products, including membership fees. Commissions are only assigned when a physical payment is made. During a free trial, no commission will be assigned until the payment is successfully processed - whether it's at the end of the trial or through manual payment. If payment fails after the trial, no commission will be assigned. Similarly, no commission is assigned at the start of a trial period without payment.