The promotion will run from today until October 23 while the coupon is valid until November 1st
Starting today Rocket League is free to play, and as part of the promotion, Epic Games has decided to donate $10 credits to be spent on the Epic Games Store if you go to download the game from them.
The move apparently comes as an attempt to get PC gamers from Steam on their platform. Rocket League is no longer on Steam but whoever bought it from there can continue to play it, and that version will continue to receive support and updates.
This is not the first time Epic has undertaken such campaigns, every week it delivers various free games. The most famous is GTA V, which was downloaded so much that it crashed Epic servers.