Steve,When using Customer Attributes, you'll want your CSV file to match
against a declared ID, not the Marketing Cloud ID (mid). This declared
ID is also called an Alias ID. More can be read about this ID in this
article. Keying off the declared ID rather than the MID allows you to
give the same user the same experience across multiple devices. This is
also the reason the AuthState is needed (see below).Additionally, a
common issue I see with customers trying to use Customer Attributes in
Targe...