The metadata section (item 2, above) describes the properties of each custom column - including a unique ID that can be referenced in the results array (where the actual values are stored).

Within the metadata section, the dynamic_fields collection defines 4 metric types, per conversion rule:

Conversions – The total number of conversions
CVR (Conversion Rate) – Conversions/Impressions x 100 (As a %)
CPA (Average Cost Per Action) – Total Spent/Conversions
Value (Conversion Value in $) - The sum of conversion values, based on the conversion value parameter. If the conversion value parameter is empty, this value will be 0.

The dynamic_fields collection breaks down each one of the 4 metrics further, showing separate metadata definitions for overall, clicks and views. This makes up a total of 12 metadata definitions.

An example follows below.