How to require specific eth amount in purchase function on erc721 smart contract

Question

I want each NFT to cost .02 ETH to mint. There is a constructor uint256 variable called price, but I'm not sure what to do with it since it doesn't correspond to eth.

I just need to know what to add to the 'purchase' function in order to make it cost a certain amount PER nft. Meaning it'll be multiplied if they mint more than 1 in the transaction.

Here is the contract: https://rinkeby.etherscan.io/address/0x3F4d03C071bB0C2B7748417ED03D04C034687013#readContract

Answer 1

From the purchase function _price is the price of each token in wei.

function purchase(uint numberOfTokens) public payable {
    require(numberOfTokens <= 50, "Can only purchase a maximum of 50");
    require(_price.mul(numberOfTokens) <= msg.value, "Ether value sent is not correct");
    mintToSender(numberOfTokens);
}

If you want each token to cost 0.02 eth then you have to set _price to 0.02 ether.