Today - additional bids must include both a seller URL and a top-level seller URL; both seller and top-level seller fields must be known by the buyer (and cannot be filled by an intermediary seller) since the entire additional bid must be signed by a buyer’s private key. This is contrary to the typical buyer-seller relationship where a buyer only has a relationship with their direct seller (but not a seller removed further away from the buyer, such as an ad server or a header bidding wrapper).

In standard FLEDGE bidding, buyers have control over which sellers or top-level sellers that they bid on via the browserSignals in generateBid. However, buyers can choose to ignore these seller signals and bid into any seller or top-level seller. In contrast, additional bids require that buyers explicitly specify the seller and top-level seller. We propose that additional bids’ seller fields should include an optional wildcard ‘*’ which matches any seller or top-level seller.