ChargeCents is what month one costs after the discount, in USD cents, totalled over the seats quoted. On team that is a multiple of the seat count, so it is not ListCents minus DiscountCents.
DiscountCents is what the promo takes off month one, in USD cents. The promo rate reaches at most TeamSeatCap seats; seats past the cap bill at full list and add nothing here. It is arithmetic only — quoting credits nothing, counts nothing and reserves nothing.
Plan is the tier priced, lower-cased and trimmed: pro, max or team. Unlike a redemption's plan this one comes from the REQUEST — quoting has no side effects, so it will happily price a plan the caller does not hold.
Reason is why Eligible is false, drawn from: "promo redemption is closed" (the subsystem is off, which is how it ships), "promo redemption cap reached", "promo is not active", "plan is free or unknown; nothing to discount", "promo does not cover plan
Seats is the seat count priced; a request of 0 or less was read as 1. It only bites on team, the one per-seat plan — pro and max are single-seat and ignore it.