We have received several support requests regarding CustomerID that is used in the adCenter API SOAP header. I was hoping to clear up some of the questions for those of you upgrading to adCenter API version 6 by our October 31 deadline. The CustomerID is only needed for a small number of adCenter API calls, specifically the targeting library calls such as CampaignManagement AddTargetsToLibrary. It is also needed if you have an editorial bypass in place, such as a trademark term. If you are not using the target libraries or don't have any editorial exclusions, you won't need it, and you can leave the value as null or an empty string, which would produce a SOAP element such as:
<h:CustomerId i:nil="true" xmlns:h="https://adcenter.microsoft.com/v6" xmlns:i="http://www.w3.org/2001/XMLSchema-instance"/>
If you are using the targeting libraries, then you will need to contact support to retrieve your CustomerID.
If you are a reseller and creating customers via the call to CustomerSignUp, then you would want to store the CustomerID that is returned by this method.
There is more information on the CustomerID and other identifiers on MSDN at:
http://msdn.microsoft.com/en-us/library/dd776532.aspx
Jeff Dillon, API Support