Return the unique customer identifier associated with the current device.

String customerID = Nami.getExternalIdentifier()
NSString *externalID = [Nami getExternalIdentifier];
val customerId: String? = Nami.getExternalIdentifier()
String customerId = Nami.getExternalIdentifier();
NativeModules.NamiBridge.getExternalIdentifier( (customerID) => { } )
String customerId = await Nami.getExternalIdentifier();
var customerID = Nami.GetExternalIdentifier();


A string of the external identifier that Nami has stored. Returns null if no id has been stored, including if a string was passed to setExternalIdentifier that was not valid.