CPA – Cost Per Action, which means that you only have to pay for conversions.
Before unlocking CPA option, you have to do create CPM Goal or CPC Goal campaign and initiate testing period.
First, you need to setup postback for your campaigns in order to track conversions:
Then you need to create CPM Goal or CPC Goal campaign with 1 country and goal price:
Upon creation, the "Testing" stage begins. More on that below.
After successful test run, you're good to go: CPA campaign could be created.
There'a an option to choose either a single price for all of your targeted countries, or you may set up multiple pricing policies. For example, Price 1 would be $2 for Belgium and Price 2 would be $5 for Germany and Netherlands.
Bear in mind that before launch, your campaign must pass the test period, during which it will be granted "Testing" status.
During "Testing" stage of your campaign, a certain amount of funds is reserved on your balance, which could be calculated by the formula:
= (Price 1 + Price 2 +... + Price n) * 10
Price 1 = $2
Price 2 = $5
Reserved balance is: (2+5)*10=$70