How to mint NFTs using Crossmint API

Hi,
I am developing NFT marketplace integrating Crossmint API now.
I added crossmintPayButton to my website like the following.

import { CrossmintPayButton } from '@crossmint/client-sdk-react-ui';
...
<CrossmintPayButton
    className='xmint-btn'
    clientId={process.env.NEXT_PUBLIC_CROSSMINT_CLIENT_ID!}
      environment='staging'
      mintConfig={{
      type: 'erc-721',
      totalPrice: price * mintQuantity,
      _price: price
      _quantity: mintQuantity,
      _metadata: {
        name: "Test NFT",
        description: "This is my test NFT!",
        image: "..."
      }
    }}
/>

How can I write mint function of contract to mint NFTs?
Please, help me.