We bill customers based on the volume of messages sent to and received from individual recipients. This
means you aren't charged more for recipients who answer fewer questions or messages in that month. For
example, if in a given month you have 50 recipients who fall in the $1 tier and 50 who fall in the $3 tier,
we will bill for those recipients based on their respective tiers at (50 * $1) + (50 * $3) = $200.