About Epic Games's Royalty Fee: How is it tracking our game sales/earns

Our first project getting to ready soon. So we searching about Epic Games’s fee

[FONT=“Motiva Sans”]“UE4 is free to use, with a 5% royalty on gross product revenue after the first $3,000 per game per calendar quarter from commercial products. Read the EULA FAQ for more details. Contact us if you require custom terms.”[FONT=Helvetica,Arial,Verdana,sans-serif][SIZE=2][COLOR=#007000] [/SIZE][/COLOR]in EULA

But how are they follow our game, knowledge about game in market and how much sold/earn etc. Are we need to report game’s release information or Epic Games doing this by them

Check out this post on the answerhub:
How does EPIC track my release for royalties?