In AdWords you could choose to optimize your automated bidding on "Converted clicks" or "Conversions." 
AdWords recently announced that we're saying goodbye to "Converted clicks" in favor of “Conversions,” which offers much more flexibility and measurement options. As a result, we’re updating the API.
The 
conversionOptimizerMode attribute of the 
Customer.conversionTrackingSetting allowed you to set 
ONE_PER_CLICK ("Converted clicks") or 
MANY_PER_CLICK ("Conversions") at the account level.
Starting on September 21, 2016, all AdWords accounts will be automatically migrated to set 
conversionOptimizerMode to 
MANY_PER_CLICK, and new mutate operations to change this setting will fail with 
RequestError.INVALID_INPUT.
Prior to 
September 21, 2016, ensure your 
CustomerService mutate requests do not attempt to modify the value of 
conversionOptimizerMode. You can also migrate your accounts before the migration by setting 
conversionOptimizerMode to 
MANY_PER_CLICK.
If you have any questions, please let us know on the 
forum.
-Mike Cloonan, AdWords API Team