How do I get the PRO version?

TL;DR:

Just attempt to use any paid feature in the app or use the Try Now button in the Connect screen, and you'll be presented with a popup to make a payment. If you don't see any paid features, then your car must not support them.

Full instructions:

Our paid functionality is available as an in-app purchase inside the same free-to-download app. You must be connected to a car that's compatible with the paid functionality in order to purchase it. There are 3 ways to do it:

• Option A: Go into “Customize”, pick a setting you want to change, pick a new value for it and click “Save”. Then see below.
• Option B: Go into “Diagnose” and if your vehicle has any manufacturer-specific fault codes, click on the fault code or “Reset” button. Then see below.
• Option C: Go into "Service", pick a service tool you want to use, and attempt to use it. Then see below.
• Option D: Go into "Live data", pick a live data you want to read, and click "Buy Pro". Then see below.

In all cases, if you’re using a generic WiFi adapter (not the Carista adapter), you’ll get a message asking you to unplug the adapter; do that, give the phone about 30sec to regain internet connectivity, and then click “OK, I disconnected”. If you’re using the Carista adapter, you don’t need to disconnect. Next, you’ll see a new screen that shows your purchase options. On iOS, you may get prompted to enter your Apple ID password; don’t worry, you’re not yet purchasing, so go ahead and enter those. Pressing "Buy now" will take you through Google’s or Apple’s in-app purchase process. All payment information is handled through their respective platforms, so please direct any payment-related questions to Google or Apple. When you’re done with the payment, all functionality in the app will be unlocked for you, so go ahead and start using it.