FormBricks REST API Resolving Expected Date, Received String Error

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Introduction

Hey guys! Ever run into a frustrating error while trying to create surveys using the FormBricks REST API? Specifically, have you ever seen that dreaded “bad request” error when dealing with createdAt and updatedAt fields? You're not alone! This article dives deep into a common issue encountered when using the FormBricks REST API – the “Expected date, received string” error. We'll break down the problem, explore why it happens, and provide practical solutions to get your survey creation process back on track. If you've been scratching your head over this, or if you're just starting with FormBricks and want to avoid potential pitfalls, this guide is for you. We’ll cover everything you need to know to handle date formats correctly and ensure your API requests are smooth sailing.

Understanding the Issue: Expected Date, Received String

The core issue revolves around how the FormBricks API expects date values to be formatted. When you send a POST request to create a survey, you might include trigger details that contain date fields like createdAt and updatedAt. The API is quite particular about these dates; it expects them in a specific format, and if it receives a string that doesn't match this format, it throws a “bad request” error. This usually manifests as an “Expected date, received string” message, which can be pretty cryptic if you're not familiar with the intricacies of API date formatting. Think of it like trying to fit a square peg into a round hole – the API simply can’t process the string as a valid date. So, why does this happen? Well, often, it's because the date is being sent as a plain string without the correct formatting. Dates and times in APIs need to be standardized to ensure that different systems can understand them. This standardization usually involves using a specific string format that includes the year, month, day, hours, minutes, and seconds, often along with timezone information. Without this proper formatting, the API can’t parse the string and convert it into a date object, leading to our error. The key takeaway here is that the “Expected date, received string” error is a format mismatch. We need to ensure that the dates we send to the FormBricks API are in the exact format it expects. Let’s delve deeper into the common causes and then explore how to fix them.

Common Causes of the Error

Okay, so we know the error is about date formatting, but what exactly causes it? There are several common culprits that lead to the “Expected date, received string” error when using the FormBricks REST API. Let's break them down:

  1. Incorrect Date Format: This is the most frequent cause. The FormBricks API, like many APIs, expects dates to be formatted in a specific way, often using the ISO 8601 standard. A typical ISO 8601 date format looks something like this: YYYY-MM-DDTHH:mm:ss.sssZ (e.g., 2025-07-29T11:26:22.000Z). If you send a date in any other format—say, MM/DD/YYYY or DD-MM-YYYY—the API won't recognize it as a valid date, and you'll get the error. The T separates the date and time, and the Z indicates that the time is in UTC (Coordinated Universal Time). Missing any of these components or using a different separator can cause issues. It’s crucial to adhere strictly to the expected format to avoid this pitfall.
  2. Missing Time Zone Information: Another common mistake is omitting the time zone information. While the API might accept a date and time, it often requires the time zone to be specified. This is usually done by appending Z for UTC or using an offset like +00:00. Without this, the API might not be able to accurately interpret the date and time, especially if your server or client is in a different time zone. Including the time zone ensures that the date and time are unambiguous and can be correctly processed by the API.
  3. Data Type Mismatch: Sometimes, the issue isn't just the format but the data type itself. Even if your date string looks correct, it might not be recognized if it's not explicitly treated as a date object in your code. For example, if you're using a programming language like JavaScript, you might need to use the Date object to ensure the date is properly formatted before sending it in the API request. Simply passing a string that looks like a date might not be enough; you need to ensure it’s a date object or a string that the API can interpret as a date.
  4. Serialization Issues: When sending data in JSON format, which is common for REST APIs, there can be issues with how dates are serialized. Some serialization libraries might not automatically convert date objects into the correct string format. This can lead to dates being sent as raw objects or in an unexpected string format. You might need to configure your serialization library to handle dates correctly, ensuring they are converted to the ISO 8601 format before being included in the JSON payload. Libraries often have settings or transformers specifically for this purpose.

By understanding these common causes, you can start to troubleshoot the “Expected date, received string” error more effectively. Now, let’s move on to how we can actually fix this issue.

Solutions and Best Practices

Alright, let's get down to brass tacks and talk about how to fix this “Expected date, received string” error. Here are several solutions and best practices you can implement to ensure your dates are correctly formatted and your FormBricks API requests go through smoothly:

  1. Use the Correct Date Format (ISO 8601): As we've emphasized, the most critical step is to ensure your dates are in the ISO 8601 format. This format is the de facto standard for APIs and is widely recognized. The format typically looks like this: YYYY-MM-DDTHH:mm:ss.sssZ. Let’s break it down:

    • YYYY: Four-digit year (e.g., 2025)
    • MM: Two-digit month (01-12)
    • DD: Two-digit day (01-31)
    • T: Separator between the date and time
    • HH: Two-digit hour (00-23)
    • mm: Two-digit minute (00-59)
    • ss: Two-digit second (00-59)
    • sss: Milliseconds (optional, but often included)
    • Z: Indicates UTC time (or you can use an offset like +00:00)

    For example, July 29, 2025, at 11:26:22 AM UTC would be: 2025-07-29T11:26:22.000Z. Make sure your code generates dates in this format before sending them to the API. Most programming languages have built-in functions or libraries to help with this.

  2. Utilize Date Formatting Libraries: Don't reinvent the wheel! Most programming languages have excellent libraries for handling date formatting. These libraries can save you a ton of time and reduce the risk of errors. Here are a few examples:

    • JavaScript: date-fns, moment.js (though Moment.js is in maintenance mode, date-fns is a great alternative)
    • Python: datetime (built-in), arrow, pendulum
    • Java: java.time (built-in), Joda-Time
    • C#: DateTime (built-in), Noda Time

    For instance, in JavaScript using date-fns, you can format a date like this:

    import { format } from 'date-fns';

const now = new Date();
const formattedDate = format(now, 'yyyy-MM-ddTHH:mm:ss.SSSZ');
console.log(formattedDate); // Output: 2025-07-29T11:26:22.000Z (example)

  3. Ensure Correct Serialization: When sending data as JSON, ensure that your date objects are correctly serialized into ISO 8601 strings. Many JSON serialization libraries have settings to handle dates properly. For example, in JavaScript, you can use the JSON.stringify() method, but you might need to write a custom replacer function to format dates:

    const data = {
  createdAt: new Date(),
  updatedAt: new Date(),
};

const json = JSON.stringify(data, (key, value) => {
  if (value instanceof Date) {
    return format(value, 'yyyy-MM-ddTHH:mm:ss.SSSZ');
  }
  return value;
});

console.log(json);

    Some libraries, like axios, can automatically serialize dates if configured correctly. Check the documentation for your chosen library to see how to handle date serialization.

  4. Check Your API Request Payload: Before sending the request, double-check the payload you're sending to the FormBricks API. Use tools like your browser's developer console or a dedicated API testing tool (like Postman or Insomnia) to inspect the request body. This will allow you to see exactly what data is being sent, including the date formats. It's much easier to catch a formatting error by inspecting the payload than by debugging the code after the error occurs.

  5. Validate API Responses: Implement error handling in your code to catch API errors and log them. When you receive a “bad request” error, inspect the error message closely. It often provides clues about what went wrong, such as which field caused the issue. Logging these errors can help you quickly identify and fix date formatting problems.

  6. Use UTC Time: To avoid time zone-related issues, it’s best practice to store and transmit dates in UTC. This eliminates ambiguity and ensures that dates are interpreted consistently across different systems. Convert your dates to UTC before sending them to the API, and parse UTC dates when receiving them.

By following these solutions and best practices, you can significantly reduce the chances of encountering the “Expected date, received string” error and ensure your FormBricks API integrations are robust and reliable.

Practical Examples and Code Snippets

Let's solidify our understanding with some practical examples and code snippets. These examples will demonstrate how to format dates correctly in different programming languages and how to handle them in API requests.

JavaScript Example

Here’s how you can format dates using date-fns and send them in a JSON payload using fetch:

import { format } from 'date-fns';

async function createSurvey(surveyData) {
  const formattedCreatedAt = format(new Date(), 'yyyy-MM-ddTHH:mm:ss.SSSZ');
  const formattedUpdatedAt = format(new Date(), 'yyyy-MM-ddTHH:mm:ss.SSSZ');

  const payload = {
    ...surveyData,
    triggers: [
      {
        createdAt: formattedCreatedAt,
        updatedAt: formattedUpdatedAt,
      },
    ],
  };

  try {
    const response = await fetch('https://api.formbricks.com/surveys', {
      method: 'POST',
      headers: {
        'Content-Type': 'application/json',
      },
      body: JSON.stringify(payload),
    });

    if (!response.ok) {
      console.error('API Error:', response.status, await response.text());
      return;
    }

    const data = await response.json();
    console.log('Survey created:', data);
  } catch (error) {
    console.error('Fetch Error:', error);
  }
}

// Example usage
const surveyData = {
  name: 'Customer Feedback Survey',
  description: 'Gather feedback from customers.',
};

createSurvey(surveyData);

In this example, we use date-fns to format the createdAt and updatedAt dates into the ISO 8601 format before including them in the JSON payload. This ensures that the API receives the dates in the expected format.

Python Example

Here’s how you can format dates using the datetime module and send them in a JSON payload using the requests library:

import datetime
import requests
import json

def create_survey(survey_data):
  formatted_created_at = datetime.datetime.utcnow().isoformat() + 'Z'
  formatted_updated_at = datetime.datetime.utcnow().isoformat() + 'Z'

  payload = {
    **survey_data,
    'triggers': [
      {
        'createdAt': formatted_created_at,
        'updatedAt': formatted_updated_at,
      }
    ]
  }

  try:
    response = requests.post(
      'https://api.formbricks.com/surveys',
      headers={'Content-Type': 'application/json'},
      data=json.dumps(payload)
    )

    response.raise_for_status()  # Raise an exception for HTTP errors

    data = response.json()
    print('Survey created:', data)
  except requests.exceptions.RequestException as e:
    print('API Error:', e)

# Example usage
survey_data = {
  'name': 'Customer Feedback Survey',
  'description': 'Gather feedback from customers.'
}

create_survey(survey_data)

In this Python example, we use the datetime module to get the current UTC time and format it as an ISO 8601 string. We then include this formatted date in the JSON payload sent to the FormBricks API.

Java Example

Here’s how you can format dates using the java.time API and send them in a JSON payload using the HttpURLConnection class:

import java.net.URI;
import java.net.HttpURLConnection;
import java.net.URL;
import java.nio.charset.StandardCharsets;
import java.time.Instant;
import java.time.ZoneOffset;
import java.time.format.DateTimeFormatter;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import com.fasterxml.jackson.databind.ObjectMapper;

public class FormBricksAPI {

    public static void createSurvey(Map<String, Object> surveyData) throws Exception {
        DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd'T'HH:mm:ss.SSS'Z'").withZone(ZoneOffset.UTC);
        String formattedCreatedAt = formatter.format(Instant.now());
        String formattedUpdatedAt = formatter.format(Instant.now());

        List<Map<String, String>> triggers = List.of(Map.of("createdAt", formattedCreatedAt, "updatedAt", formattedUpdatedAt));
        surveyData.put("triggers", triggers);

        ObjectMapper mapper = new ObjectMapper();
        String payload = mapper.writeValueAsString(surveyData);

        URL url = URI.create("https://api.formbricks.com/surveys").toURL();
        HttpURLConnection connection = (HttpURLConnection) url.openConnection();
        connection.setRequestMethod("POST");
        connection.setRequestProperty("Content-Type", "application/json");
        connection.setDoOutput(true);

        try (var os = connection.getOutputStream()) {
            byte[] input = payload.getBytes(StandardCharsets.UTF_8);
            os.write(input, 0, input.length);
        }

        try (var br = new java.io.BufferedReader(
                new java.io.InputStreamReader(connection.getInputStream(), StandardCharsets.UTF_8))) {
            StringBuilder response = new StringBuilder();
            String responseLine = null;
            while ((responseLine = br.readLine()) != null) {
                response.append(responseLine.trim());
            }
            System.out.println(response.toString());
        }
    }

    public static void main(String[] args) throws Exception {
        Map<String, Object> surveyData = new HashMap<>();
        surveyData.put("name", "Customer Feedback Survey");
        surveyData.put("description", "Gather feedback from customers.");

        createSurvey(surveyData);
    }
}

In this Java example, we use the java.time API to format the dates into the ISO 8601 format. The DateTimeFormatter is used to specify the desired format, and the dates are formatted in UTC. The Jackson library (com.fasterxml.jackson.databind.ObjectMapper) is used to serialize the data into JSON format.

C# Example

Here’s how you can format dates using the DateTime struct and send them in a JSON payload using the HttpClient class:

using System;
using System.Net.Http;
using System.Text;
using System.Threading.Tasks;
using Newtonsoft.Json;

public class FormBricksAPI
{
    public static async Task CreateSurvey(dynamic surveyData)
    {
        var formattedCreatedAt = DateTime.UtcNow.ToString("yyyy-MM-ddTHH:mm:ss.fffZ");
        var formattedUpdatedAt = DateTime.UtcNow.ToString("yyyy-MM-ddTHH:mm:ss.fffZ");

        surveyData.triggers = new[]
        {
            new
            {
                createdAt = formattedCreatedAt,
                updatedAt = formattedUpdatedAt
            }
        };

        var jsonPayload = JsonConvert.SerializeObject(surveyData);

        using (var httpClient = new HttpClient())
        {
            var content = new StringContent(jsonPayload, Encoding.UTF8, "application/json");
            var response = await httpClient.PostAsync("https://api.formbricks.com/surveys", content);

            if (!response.IsSuccessStatusCode)
            {
                Console.WriteLine({{content}}quot;API Error: {response.StatusCode} - {await response.Content.ReadAsStringAsync()}");
                return;
            }

            var responseContent = await response.Content.ReadAsStringAsync();
            Console.WriteLine({{content}}quot;Survey created: {responseContent}");
        }
    }

    public static async Task Main(string[] args)
    {
        dynamic surveyData = new
        {
            name = "Customer Feedback Survey",
            description = "Gather feedback from customers"
        };

        await CreateSurvey(surveyData);
    }
}

In this C# example, we use DateTime.UtcNow.ToString("yyyy-MM-ddTHH:mm:ss.fffZ") to format the dates into the ISO 8601 format. We then use JsonConvert.SerializeObject from the Newtonsoft.Json library to serialize the data into JSON format. This ensures the dates are correctly formatted when sent to the FormBricks API.

These examples demonstrate how to handle date formatting in different languages, ensuring that you send the dates in the format expected by the FormBricks API. By using these code snippets as a reference, you can avoid the “Expected date, received string” error and create surveys successfully.

Conclusion

Dealing with API errors can be frustrating, but understanding the root cause and implementing the right solutions can make the process much smoother. The “Expected date, received string” error in the FormBricks REST API is a common issue, but as we’ve seen, it’s easily resolved by ensuring dates are formatted correctly. Remember, the key is to use the ISO 8601 format (YYYY-MM-DDTHH:mm:ss.sssZ), utilize date formatting libraries, ensure correct serialization, and always validate your API requests and responses. By following these best practices and using the code examples provided, you can avoid this error and build robust integrations with the FormBricks API. So go ahead, create those surveys, and gather that valuable feedback without the headache of date formatting issues! Happy coding, and may your API requests always be successful!