Sorry for the delay - I needed to set up a test environment for this and I’ve not had the time to do that until today!
I think the issue is that you’re expecting the field itself to be available for mapping. Instead the Field parameter in the output bundle is set to the name of the field that was caught by Watch Record Fields.
This is as a result of the way the Saleforce API works - rather than returning all fields, it just gives you the value of the field that changed.
Here’s an example of the output for a Salesforce Account record where a custom field Active__c had changed.
