The P9 isn't on the supported devices list
However, Fitbit say that if the P9 "meets the operating system requirements as listed on that page, you will likely still be able to set up, sync and use Fitbit products".
As the P7 and P8 are supported devices I would imagine the P9 meets the requirements but you would need to double check.
If you order it from somewhere like Amazon you will be able to return it easily if it turns out not to be compatible.
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A warm welcome to the Community @Aflmoreira and @seantnash thanks for the input.
I just wanted to let you know that I have moved your post from the Charge 3 board to the Android app board, since I think that here you will be able to see more related topics about the Fitbit app.
Now about your compatibility inquiry, Fitbit is compatible with more than 200 of the most popular Android, iOS and Windows mobile devices.
The full list of compatible devices with confirmed compatibility can be found here. If a device isn’t listed it doesn’t mean it won’t work with a Fitbit tracker or smartwatch. We routinely test new devices to ensure full compatibility with Fitbit devices and the Fitbit App, and are constantly working to confirm compatibility with new phone models.
A majority of Android phones running version 4.4 or higher will work with our products, however we cannot guarantee optimal performance on devices for which we have not tested and confirmed compatibility.
Keep the stepping up! 
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