Flow Board 2 Trial License
It should be very easy to acquire and set a trial license for Flow Board (or any app). Listed below is a walk through of the screens you'll see during this process.  However if the Atlassian trial license workflow is not behaving properly an alternative method is to go to the listing on the MarketPlace and click on the button "Trial License".
Walk thru of trial license screens
This is how installation of the app trial license should look. However sometimes the Atlassian platform has issues which can cause it to look different. In those cases you can either retry or use the screen above to acquire a trial license.
Success !
You can manually update your license if needed by clicking the pencil icon