Currently, the Cost Management API documentation does not have any details or example about the delta parameter. It only informs that a string value is expected, but no example is provide or list of accepted values.

Below is how it is currently described:

Name	Type	Description
delta   string	Toggle to include delta values in report. 

 
Require the API documentation page to be updated with more details about the delta parameter like accepted / valid values and a few examples.