Hi! The CC0 license applies only to the free pack I have available.
For all paid packs, they come with a custom license, which is detailed in the readme file. You can absolutely use the assets in commercial projects, modify, adapt, or change them to suit your needs. The only two restrictions are that you cannot resell the assets as a standalone product, and they shouldn’t be used for harmful purposes. Other than that, you're free to use them however you like! No need for credits or anything else—you've purchased it, and seeing your awesome projects is the best reward I could ask for! 😄