Validate creditcard with c#

validateCreditCard.cs

private static bool ValidateCreditCard(string? creditCard)
    {

        try
        {
            _ = long.Parse(creditCard ?? "");
        }
        catch (Exception)
        {
            return false;
        }

        if (string.IsNullOrEmpty(creditCard)) return (false);

        int[] digits = new int[creditCard.Length];
        for (int i = 0; i < creditCard.Length; i++)
        {
            digits[i] = Convert.ToInt32(creditCard.Substring(i, 1));
        }

        for (int i = digits.Length - 2; i >= 0; i -= 2)
        {
            int results = digits[i] * 2;
            if (results > 9)
            {
                results -= 9;
            }
            digits[i] = results;
        }

        int sum = 0;
        foreach (int digt in digits)
        {
            sum += digt;
        }

        return (sum % 10 == 0);
    }