Let's set up the "Audience". Go to the "Configure" => "Audiences" section. And click "New audience".
Then click "Create a custom audience".
Enter a name for the new audience (for example, "Unique_calls"). After that, set up the conditions:
Click "Events" and select Ringostat_calls.
Add the "call_unique" parameter.
For the conditions, select "exactly matches (=)" and set the value: "1".
Then specify the "Audience Trigger" without spaces. For example, "Unique_call".
Save the audience
The last step is to set up conversion for this audience. Go to "Configure" => "Conversions". And click "New conversion event".
Give the conversion name the same as the audience trigger — "Unique_call" and save.
Conversion events are automatically enabled.