On 
January 31, 2020, the 
AdWords API and 
Google Ads API will no longer allow positive user list criteria in 
Smart Display campaigns. 
What happens to my existing Smart Display Campaigns?
Existing Smart Display campaigns with positive user list targeting:
  - Will continue to serve without interruption.
- Will no longer allow adding a positive CampaignCriterionorAdGroupCriterionwith a user list criterion.
- Will no longer serve if the ad group is paused and then restarted.
What code do I need to change?
Please update your code that manages Smart Display campaigns per the following updated validation rules:
You will receive a 
CANNOT_TARGET_CRITERION error if you try to add one of these criteria.
Why is this changing?
Adding these criteria for Smart Display campaigns was never formally supported as outlined in our 
Smart Display campaigns guide. Additional validation is being put in place now to make sure that these values are not being set. Please see 
the guide for supporting criteria.
If you have any questions while updating your code, please reach out to us on our Google Ads API and AdWords API 
forum.
 Nadine Wang, Google Ads API Team
 Nadine Wang, Google Ads API Team