Template:WarnSearchUppercaseFieldsForCRMObjects
From LongJump Support Wiki
Important:
When searching the CRM Objects using the REST API, you need to use the (mostly uppercase) REST versions of the field names when specifying Field Lists and Filter Expressions in the Dynamic Search Parameters. Those field names are returned, as well. For example: OWNERID.When you do an HTTP GET, on the other hand, tags are returned in lowercase, with underscores. For example: owner_id. Those tag names must be specified when doing an HTTP PUT. Those are also the field names you use in the GUI and in the Java APIs.