To guarantee accuracy and lower failure rates in digital payment systems, a UPI (Unified Payments Interface) ID must be validated before a transaction is started. Without revealing any critical implementation details, this article describes how to integrate a UPI ID validation API using JavaScript and C# (ASP.NET). To demonstrate, we'll use a fictitious endpoint.

Why Validate UPI IDs?

• Avoid transaction failures due to incorrect UPI IDs
• Improve user experience by providing real-time feedback
• Ensure the UPI ID belongs to the correct customer

Technologies Used

• C# (ASP.NET WebForms/Backend)
• JavaScript (AJAX for frontend calls)
• JSON for data communication
• Dummy API endpoint (replace with actual provider)

Example API Request
POST https://dummyapi.example.com/v1/payments/validate/vpa
Content-Type: application/json
{
"vpa": "user123@dummyupi"
}

Successful Response
{
  "vpa": "user123@dummyupi",
  "customer_name": "John Doe",
  "success": true
}

Invalid UPI Response
{
  "error": {
    "code": "BAD_REQUEST_ERROR",
    "description": "Invalid VPA. Please enter a valid Virtual Payment Address",
    "source": "customer",
    "step": "payment_initiation",
    "reason": "invalid_vpa"
  }
}

Backend Implementation (C#)
Here’s a simplified C# function to validate a UPI ID via HTTP POST.
public static string ValidateUPIID(string upi)
{
string responseJson = "";
try
{
    var requestObj = new { vpa = upi };
    string requestJson = new JavaScriptSerializer().Serialize(requestObj);

    HttpWebRequest request = (HttpWebRequest)WebRequest.Create("https://dummyapi.example.com/v1/payments/validate/vpa");
    request.Method = "POST";
    request.ContentType = "application/json";

    byte[] data = Encoding.UTF8.GetBytes(requestJson);
    using (var stream = request.GetRequestStream())
    {
        stream.Write(data, 0, data.Length);
    }

    using (HttpWebResponse response = (HttpWebResponse)request.GetResponse())
    using (StreamReader reader = new StreamReader(response.GetResponseStream()))
    {
        responseJson = reader.ReadToEnd();
    }

    if (responseJson.Contains("success"))
    {
        var jsonObj = new JavaScriptSerializer().Deserialize<UPIResponse>(responseJson);
        return jsonObj.success ? $"success - {jsonObj.customer_name}" : "failed - ";
    }
    else if (responseJson.Contains("error"))
    {
        var errorObj = new JavaScriptSerializer().Deserialize<UPIErrorResponse>(responseJson);
        string errDesc = !string.IsNullOrEmpty(errorObj.error.description) ? errorObj.error.description : "Invalid VPA";
        string errReason = !string.IsNullOrEmpty(errorObj.error.reason) ? errorObj.error.reason : "invalid_vpa";
        return $"reason - {errDesc} - {errReason}";
    }

    return "failed - unknown error";
}
catch (Exception ex)
{
    return "error - " + ex.Message;
}
}

public class UPIResponse
{
public string vpa { get; set; }
public string customer_name { get; set; }
public bool success { get; set; }
}
public class UPIErrorResponse
{
public UPIError error { get; set; }
}
public class UPIError
{
public string code { get; set; }
public string description { get; set; }
public string source { get; set; }
public string step { get; set; }
public string reason { get; set; }
}

JavaScript Frontend (AJAX Call)
<div class="bid-content-common bid-content-3">
<label class="upiid-lble">UPI ID</label>
<input id="txtupiid" runat="server" type="text" placeholder="Enter the UPI ID"
       onchange="UPIIDtxtboxchanges()" onblur="handleBlur()" />
<span id="upidtxt"></span>
<input id="upidvalidation" type="hidden" />
<button id="applybtn">Apply</button>
</div>

<script>
function UPIIDtxtboxchanges() {
    var applybtn = document.getElementById("applybtn");
    var upitxt = document.getElementById("upidvalidation");
    var txtbutton = document.getElementById("txtupiid");
    var verifytxt = document.getElementById("upidtxt");

    upitxt.value = 'Verify';
    upitxt.style.backgroundColor = "#F0F0F0";
    upitxt.style.border = "2px solid #979F6E";
    upitxt.style.color = "black";
    verifytxt.innerText = "";
    applybtn.style.pointerEvents = "auto";
}

function handleBlur() {
    // Assuming upivalidationmethod takes a callback function
    upivalidationmethod(function (isValid) {
        if (isValid) {
            return true;
        } else {
            return false;
        }
    });
}

function upivalidationmethod(callback) {
    var upiId = document.getElementById("upiInput").value;

    $.ajax({
        type: "POST",
        url: "/your-page.aspx/ValidateUPI",
        contentType: "application/json; charset=utf-8",
        data: JSON.stringify({ upi: upiId }),
        success: function (res) {
            var status = res.d.split('-');
            if (status[0] === "success") {
                $("#message").text("Valid UPI: " + status[1]).css("color", "green");
                callback(true);
            } else {
                $("#message").text("Invalid UPI").css("color", "red");
                callback(false);
            }
        },
        error: function () {
            $("#message").text("Error validating UPI").css("color", "red");
            callback(false);
        }
    });
}
</script>

Best Practices

• Always encrypt sensitive credentials used in API headers.
• Validate and sanitize inputs to avoid injection or malformed requests.
• Log and monitor UPI validation failures for system analysis.

Conclusion
Including a UPI ID validation phase in your application guarantees a better user experience, fewer unsuccessful transactions, and more seamless payments. This procedure is made more efficient by using an API, which provides error handling and real-time customer name checks. Securely in production, substitute your real provider's information with the fake API URL and login credentials.