Need not be specified. You can define an AffiliateUserID (up to 256 characters) if you want to leverage it to better monitor your marketing efforts. If you are using the eBay Partner Network, and you provide an AffiliateUserID, the tracking URL returned by eBay Partner Network will contain the AffiliateUserID, but it will be referred to as a "customid".
See the Field Index to learn which calls use AffiliateUserID.
The value you specify is obtained from your tracking partner. For eBay Partner Network, the TrackingID is the Campaign ID ("campid") provided by eBay Partner Network. A Campaign ID is a 10-digit, unique number for associating traffic. A Campaign ID is valid across all programs to which you have been accepted.
See the Field Index to learn which calls use TrackingID.
Specifies your tracking partner for affiliate commissions. Required if you specify a TrackingID. Depending on your tracking partner, specify one of the following values. Not all partners are valid for all sites. For PlaceOffer, only eBay Partner Network and Mediaplex are valid: