this is taken from the licencing file of the free/basic pack:
"- Credit is required : (Cup Nooble)
[ Credit example : Assets -From : Sprout Lands -By : Cup Nooble ]
[ If you share your game on itch.io a link to the Asset Packs page would be very appreciated ]"
usually in asset packs you don't have to credit if you have paid enough money for the premium version, but i don't know if that's the same with this one, so i cannot confirm.
cup nooble might respond to you in some time anyway, but in-case they don't, this is here.