1. Go to the Snapchat for Business website and create an account if you don't have one already.

2. After creating a business account, you need to register as a developer. Navigate to the Snapchat Developer Portal and sign up.

3. Create a new application in the developer portal. This will give you access to your app credentials, such as the `client_id` and `client_secret`, which are necessary for authentication.

1. Follow the OAuth 2.0 authorization flow provided by Snapchat to obtain an access token. This typically involves sending a POST request to the Snapchat OAuth 2.0 token endpoint with your `client_id` and `client_secret`.

2. Handle the user authorization step, where the Snapchat account holder grants your application access to their data.

3. Exchange the authorization code for an access token.

1. Choose a programming language and set up your development environment. For example, you might choose Python and ensure you have the necessary libraries installed (`requests` for HTTP requests, `json` for JSON manipulation, etc.).

2. Import the required libraries in your script or application.

1. With the access token, make authenticated requests to the Snapchat Marketing API. Use the correct endpoint for the data you want to retrieve. For example, to fetch campaign data, you would use the campaigns endpoint.

2. Ensure you handle pagination if the data you're retrieving spans multiple pages.

3. Handle any errors or rate limiting that the Snapchat API may enforce.

1. The Snapchat API should already return data in JSON format. If not, or if additional transformation is needed, use your programming language's JSON library to parse the data.

2. If you fetched the data in another format (e.g., XML), convert it to JSON by mapping the structure accordingly.

1. Once the data is in JSON format, you can either save it to a file or use it directly within your application.

2. To save to a file, write the JSON data to a file with a `.json` extension, ensuring proper file handling (opening the file, writing to it, and closing it afterward).

Example in Python

Here's a simplified example in Python that outlines the process:

```python

import requests

import json

# Replace with your actual credentials and desired endpoint

client_id = 'your_client_id'

client_secret = 'your_client_secret'

access_token = 'your_access_token'  # Obtained from the OAuth process

api_endpoint = 'https://adsapi.snapchat.com/v1/campaigns'

# Set up headers for authorization

headers = {

    'Authorization': f'Bearer {access_token}'

}

# Fetch the data

response = requests.get(api_endpoint, headers=headers)

# Check if the request was successful

if response.status_code == 200:

    # Parse the data to JSON

    data = response.json()  

    # Save the data to a JSON file

    with open('snapchat_data.json', 'w') as json_file:

        json.dump(data, json_file, indent=4)

else:

    print(f'Error: {response.status_code}')

# Handle errors, pagination, and rate limits as needed

```

1. Test your script or application thoroughly to ensure it handles different scenarios, including error responses from the Snapchat API.

2. Iterate on your code to handle any edge cases or to add additional functionality, such as filtering or sorting the data.

Remember to adhere to Snapchat's API terms of service, including rate limits and data usage policies. It's also important to manage and secure your access tokens properly to prevent unauthorized access to your Snapchat data.