Mission Achievement Point (AP)

All you have to do is collect mission point achievement 

or people used to called it Achievement Point (AP)

Press "L" at hotkey and achievement board will show up

There you see inside the red box i had 17.700 points

How to Get Free Stamp, Goddess's Lament, and Black Fury?

Go to Dishonest Merchant Pero to find the shop

To get Seal Stamp and Goddess's Lament and the rest item

you need minimal 15.000 points

for stamp you can buy 3 per day (5g each) and lament 1 per day (10g each)

and to get Black Dragon Fury you need minimal 35.000 points

How to get Achievement Point?

You need to finish some mission from some dungeon

The red circle shows how much point you will get from finishing that mission

and you see the blue box shows the mission you haven't done yet