Drum is 100% free to use and only pay for performance. You are only charged the reward amount you specified when a referrer shares your offer with a customer that results in the completion of the transaction you defined.
Example: You offer a reward of 10% of the shopping cart total for anyone who refers a customer that makes a purchase on your site. A referrer shares your offer and the customer purchases $100 worth of goods. The referrer would earn a reward of $10.
Drum charges businesses weekly based on the total number of redemptions completed and then pays out referrers their rewards directly.