This is a customer to customer forum and not an official comm channel either to or from PowWeb. But from what I can see...
The complete affiliate agreement is located here. Payout information is listed in Section 5.
In part it states: Referral Fees will be issued approximately 45 days after the end of the month in which a Referral Fee was earned. To qualify to receive payment, your Referral Fee must be at least $25. Based solely on the discretion of PowWeb, payment may be withheld for amounts under $25.
You will only be compensated for Referrals that purchase PowWeb products via the Links you generate through the PowWeb Affiliate Console. Purchases made by Referrals who have clicked on these Links will be tracked by PowWeb for the purposes of this Affiliate Program. By altering these Links in any way, you may forfeit corresponding Referral Fees.
Note the underlined section.
Hope this helps.