If the key was part of a hardware or software bundle, make sure to reach out to that specific manufacturer's support team (e.g., NVIDIA, AMD, or the retailer who sold you the hardware) to verify that the key has been properly provisioned and is valid.

The Epic Games Launcher has stored old or corrupted data preventing a new game from activating. How to Fix Epic Games Product Activation Failed E100

If you claimed a game during a free weekend and then bought it, the launcher is likely haunted by the temporary license.

Scroll down to the section to locate your Country/Region configuration.

Log into your account and access your dashboard.