Use ClientID in Your Code
Use ClientID to control which account an object is associated with when using Marketing Cloud Enterprise, Enterprise 2.0, and Agency editions. To ensure the object is created in the right account, specify the client ID on all objects passed into the API.
When provisioning an account through the API, you can set a PartnerKey for the account to identify it externally. Reference the PartnerKey in the ClientID object PartnerClientKey property. If you don't associate PartnerKey with the account, use the ClientID objectID property with your account ID as the value.
Marketing Cloud maintains the PartnerClientKey property for legacy functionality and backwards compatibility. To avoid performance issues, we discourage the use of this property in new code or integrations. Replace this property with ClientID whenever possible.
Sample .NET Code
Authenticate to the SOAP API Using the Parent Account
Create an Account with a Partner Key
Create a ClientID
Create a List
Retrieve a List from a Specific Account
Sample PHP Code
Use ClientID in your SOAP calls differently, depending on the method. In each of these examples, notice the unique placement and usage of the Client property in the SOAP body.