How would your code change with whitelisting option? (ERC721Tradable)

[villarode]

Thank you lads, this is the best tutorial on creating an NFT contract that I've seen so far (and I've seen a few)

My question is - how would you tweak your code to incorporate the whitelisting function (along the lines of ERC721Tradable in OpenSea documentation) so that payment is actually needed for the first NFT with all consequent ones being "free"?

Many thanks in advance!!)