Update (Feb 21, 2019): clarified wording of the Clicks impact.
On 
February 27, 2019, the data returned in the 
Clicks metric for 
Showcase ads will change in order to more accurately show you the interactions with products via Showcase ads in reporting.
In the 
AdWords API and the 
Google Ads API, the 
Clicks metric (
clicks for Google Ads API) will change for the 
Shopping Performance Report and the 
Product Partition Report (
product_group_view for Google Ads API) as follows:
  - Current reporting: Clicksonly include charged clicks.
- New reporting: Clickswill report all clicks, including free clicks. As a result, you may see a change in the number of reported clicks.
If you have questions, please reach out to us on the 
forum.
 Nadine Sundquist, Google Ads API Team
 Nadine Sundquist, Google Ads API Team