The Analog photo filter set in ProCamera's photo editing studio is free, that’s why it is not listed along with the in-app purchases.
This is how to unlock the Analog filters:
Edit a photo in our studio, apply one of the Analog filters, tap Save. A window will pop up that links to free video tutorials on our YouTube Channel. Tap to confirm. Now the filter set is unlocked, and you can use the filters free of charge. Enjoy!