I Got an photography app is limited free, later on do i still have to pay it?

I have a iphone 5,
and i'm really into photography. So there's an app in instagram that person tells us the good quality of what kinda of photography apps. So that person always upload a photo and put a caption oh this photography app is limited free you better get your limited free app today, and other free photography that are NOT limited free just free.
So i'm curious if its limited free and i got the app… But its suppose to be like 0.99 or i don't know.
do i pay it or not? When it was limited free i got it, i told my friends about the photography app they say its not limited free anymore.
i know my bad english, please answer me quickly.

No. Once you downloaded an app (any app) for free you won't have to pay anything.

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