How to do Primary Sales for On-Chain Items in Unity

class ERC1155SaleState;

public ERC1155SaleState(IWallet wallet, string tokenContractAddress, string saleContractAddress, Chain chain, int[] itemsForSale)
{
    _tokenContractAddress = tokenContractAddress;
    _saleContract = new ERC1155Sale(saleContractAddress);
    _client = new SequenceEthClient(chain);
    _wallet = wallet;
    _chain = chain;
    _itemsForSale = itemsForSale;
}

public async Task<bool> UpdateSaleDetailsAsync()
{
    string paymentToken = await _saleContract.GetPaymentTokenAsync(_client);

    ERC1155Sale.SaleDetails globalSaleDetails = await _saleContract.GetGlobalSaleDetailsAsync(_client);
    BigInteger cost = globalSaleDetails.Cost;
    BigInteger supplyCap = globalSaleDetails.SupplyCap;
    int startTime = globalSaleDetails.StartTime;
    int endTime = globalSaleDetails.EndTime;
}

public async Task UpdateTokenSuppliesAsync()
{
    Dictionary<BigInteger, TokenSupply> tokenSupplies = new Dictionary<BigInteger, TokenSupply>();
    GetTokenSuppliesArgs supplyArgs = new GetTokenSuppliesArgs(_tokenContractAddress, true);
    GetTokenSuppliesReturn suppliesReturn = await Indexer.GetTokenSupplies((int) _chain, supplyArgs);

    foreach (int tokenId in _itemsForSale)
    {
        TokenSupply supply = Array.Find(suppliesReturn.tokenIDs, t => t.tokenID == tokenId);
        if (supply == null)
            continue;

        tokenSupplies.Add(supply.tokenID, supply);
    }
}

[SerializeField] private Image _image;

public async void RenderTokenImage(TokenSupply supply)
{
    _image.sprite = await AssetHandler.GetSpriteAsync(supply.tokenMetadata.image);
}

class ERC1155SaleState;

public async Task<bool> PurchaseAsync(BigInteger tokenId, int amount)
{
    string to = _wallet.GetWalletAddress();
    byte[] defaultProof = Array.Empty<byte>();

    CallContractFunction contractCall = _saleContract.Mint(to, new[] {tokenId},
    new[] {new BigInteger(amount)}, null, PaymentToken, new BigInteger(1), defaultProof);

    Transaction[] transactions = new Transaction[] { new RawTransaction(contractCall) };
    TransactionReturn result = await _wallet.SendTransaction(_chain, transactions);
    return result is SuccessfulTransactionReturn;
}

class GameWindowUI;

private ERC1155SaleState _saleState;

public async void OnPurchaseClicked(BigInteger tokenId, int amount)
{
    bool success = await _saleState.PurchaseAsync(tokenId, amount);
    if (!success) {
        OpenQrCodeView();
        return;
    }

    ShowNotification("Purchase succeeded.");
    RenderState();
}