I am trying to use the SalesForce upsert component to upsert a Contact for a given Account.

I am using the spoon UI.

I have a series of fields that includes standard Contact fields plus one custom field (say user_id__c). The series of fields also includes the AccountId for the Account parent.

I have set the Module entry field to Contact. I have set the Upsert Comparison Field to user_id__c.

The custom field user_id__c is an externalid field.

If I set the Use external is attribute to N, I get this error CANNOT_REPARENT_RECORD

If I set the Use external is attribute to Y, I get this error Unable to find object type in external key syntax! Syntax for external key is : object:externalid/lookupField

The only doc I can find about this seems to suggest I should use something like Contact:user_id__c\....

I am unclear as to which UI fields this should be entered into since there are 2. I am also unclear as to how to specify an object type.

Seems like my understanding has a few gaps in it and any help or pointers in the right direction would be appreciated.