Simple ?

Pretty sure it was once off when I got it?

$11.99 one time charge on iPhone 

It’s a one time charge for each version android or iPhone. When you get a new phone there is no additional charge to reinstall.

One time charge to buy the app. Put it on any apple device I got. 
If you have Android then it will install on any android devices you got!

One time charge for the app for that platform.

One time fee and worth every dam cent. The reticle data base/scope choice is tops. It and a good range finder make airgun life enjoyable.