Sorry for the delay, usually we are not working on weekends and that’s the reason os the cause of the delay
Regarding your question, there is nothing to download or activate any key, you are purchasing rights to remove Footer credit from the theme, there is no separate theme, pro features or anything like that, simple now you can remove footer credits from the template, this is meaning of the license described here: https://colorlib.com/wp/licence/
Sorry if it’s not clear, that’s why im here to help, there is no need to use key anywhere, you just need to buy and once you get the purchase receipt you are free to remove credits from the templates, there is no extra steps here