If you are talking about the app by Beleela, then at the 'very' bottom of the description it says
"***This is a free 30-Day trial***"
So, apparently not free.
The list of in-app purchases available indicated a complicated combination of pay-for-features and subscription plans.
A quick glance at the reviews suggests this is a recent change. Not the subscription model itself, but perhaps some of the features no longer work without a subscription. Editing files on DropBox was mentioned.