User ID for the bidder to be approved. Only bidders who have requested approval can be approved. That is, the seller cannot approve a bidder who has not requested approval. (Bidders request approval via the eBay Live Auctions Web site UI.) When you are approving bidders, if you pass in multiple BidApproval entries with duplicate UserID values, the last entry with that UserID takes precedence (and the earlier duplicate UserID entries are ignored).
See the
Field Index to learn which calls use UserID.