How to pass drop_category in hash sequence

@jayraj Chhaya : Thank u....

                      but if All functionality will not work if my hash parameter is not calculated correctly

but this is not happening if i remove 

drop_category functionality work proper if  add drop_category then error occured

Please help me what is mistake in my code...

hashVarsSeq = ConfigurationManager.AppSettings["hashSequence"].Split('|'); // spliting hash sequence from config
hash_string = "";
foreach (string hash_var in hashVarsSeq)
{
    if (hash_var == "key")
    {
        hash_string = hash_string + ConfigurationManager.AppSettings["MERCHANT_KEY"];
        hash_string = hash_string + '|';
    }
    else if (hash_var == "txnid")
    {
        hash_string = hash_string + txnid1;
        hash_string = hash_string + '|';
    }
    else if (hash_var == "amount")
    {
        hash_string = hash_string + Convert.ToDecimal(lblFeeon.Text).ToString("g29");
        hash_string = hash_string + '|';
    }
    else if (hash_var == "firstname")
    {
        hash_string = hash_string + lblNameon.Text.ToString();
        hash_string = hash_string + '|';
    }
    else if (hash_var == "productinfo")
    {
        hash_string = hash_string + productinfo;
        hash_string = hash_string + '|';
    }
    else if (hash_var == "email")
    {
        hash_string = hash_string + lblEmailIdon.Text;
        hash_string = hash_string + '|';
    }

    //else if (hash_var == "phone")
    //{
    //    hash_string = hash_string + lblMobileNo.Text;
    //    hash_string = hash_string + '|';
    //}
    else if (hash_var == "udf1")
    {
        hash_string = hash_string + lbls.Text;
        hash_string = hash_string + '|';
    }
    else if (hash_var == "udf2")
    {
        hash_string = hash_string + lblAdmForm.Text;
        hash_string = hash_string + '|';
    }
   

    else if (hash_var == "udf3")
    {
        hash_string = hash_string + txtBr.Text;
        hash_string = hash_string + '|';
    }
    else if (hash_var == "udf4")
    {
        hash_string = hash_string + lblRName.Text;
        hash_string = hash_string + '|';
    }
    else if (hash_var == "udf5")
    {
        hash_string = hash_string + txtCrName;
        hash_string = hash_string + '|';
    }

    else if (hash_var == "drop_category")                 
    {
        hash_string = hash_string + "EMI";
        hash_string = hash_string + '|';
    }

//If I  remove this code then functionality work proper

}

To pass the drop_category value in the hash sequence for PayU integration in an ASP.NET website, you need to ensure that the hash parameter is correctly calculated. The error you encountered, "Transaction failed due to incorrectly calculated hash parameter," suggests that there might be an issue with the way you are calculating the hash.

Here's an example of how you can pass the drop_category value in the hash sequence:

string hashSequence = "key|txnid|amount|productinfo|firstname|email|udf1|udf2|udf3|udf4|udf5|udf6|udf7|udf8|udf9|drop_category";
string[] hashParams = hashSequence.Split('|');

string hashString = string.Empty;
foreach (string param in hashParams)
{
    if (param.Equals("drop_category"))
    {
        // Replace 'drop_category' with the actual value you want to pass
        hashString += "your_drop_category_value" + "|";
    }
    else
    {
        // Add the other parameters to the hash string
        hashString += param + "|";
    }
}

// Calculate the hash using the hashString
string calculatedHash = CalculateHash(hashString);

// Use the calculatedHash in your payment transaction

Make sure to replace 'your_drop_category_value' with the actual value you want to pass for drop_category. Additionally, ensure that the CalculateHash method is implemented correctly to calculate the hash based on the provided hash string.