5.6Don't confuse labels with API names

The Salesforce UI might display:

External Customer ID

but integration code uses:

External_Customer_ID__c

Likewise:

Customer Enrollment

might actually be:

Customer_Enrollment__c

Your Mule/DataWeave/SOQL code normally needs the API name.

This is a common source of integration failures:

INVALID_FIELD

because somebody used a display label instead of the API field name.