Not all Google Analytics metrics and dimensions can be queried together. You can check if a dimension and metric combination is valid from within Google's documentation.
Navigate to the Dimensions & Metrics Reference, in the Core Reporting API documentation.
In our example, we want to see which metrics we can query with eventAction. We'll click the plus sign to expand the Event Tracking table, which is where the eventAction dimension is located.
Once it's expanded, we'll hover over ga:eventAction to reveal a checkbox, and check it. We want to check which metrics we can use in the Ecommerce table, so we've expanded the Ecommerce table to compare.
As you can see, some of the metrics in the Ecommerce table are greyed out - this means we can't query them with eventAction. You can query any metric that is not greyed out with eventAction.