To be able to track app install and other app related event, the app should be integrated with Branch.io.
Tracking your app conversion:
Step 1: Go to Offer > Create offer.
Step 2: Fill in the details of the offer.
Step 3: Use the Tracking link from Branch.io for the Default Offer URL.
Step 4: Set the conversion tracking to "Server Postback w/ Transaction ID"
Step 5: Click "Add Offer".