App Integration Guide (Developers)

How to create an action to upload a file (Multipart/form-data)

Pabbly Connect Team•Updated Aug 18, 2026•3 min read

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API to Upload File (multipart/form-data) Documentation

Overview

This API is designed to process POST requests, retrieve files from URLs, and upload them to a specified endpoint using the multipart/form-data format. The API validates incoming requests with an API key and supports dynamic headers, endpoint configuration, and additional body parameters.

Purpose

This API acts as a middleware service, facilitating secure file transfers to any API that supports multipart/form-data based file uploads. It:

Validates incoming requests based on a provided API key.
Fetches files from specified URLs, resolving the correct content type and file extension.
Constructs a multipart/form-data payload to upload files to a designated endpoint.
Forwards headers and data to the target endpoint using the specified HTTP method.

How It Works

The API handles incoming HTTP POST requests and processes the following:

Request Validation:
- Validates the API key against a predefined value (CHECK_API_KEY).
Body Parsing:
- Accepts a JSON body containing fields like file_url, endpoint, and method.
File Retrieval and Processing:
- Fetches the file from the provided file_url.
- Determines the content type and file extension using headers or URL parsing.
Multipart Data Construction:
- Creates a multipart/form-data payload with additional body parameters and the retrieved file.
Forwarding to the Endpoint:
- Uses the provided endpoint and method to send the request, including the specified headers and payload.

Configuration in Pabbly

Configure an HTTP Request in Pabbly:

Navigate to the Pabbly Connect Developer platform and go to the "Actions" section to set up the action.
Method: Set the method as POST.
URL: Enter the URL "https://multipartformdata-fileupload.pabbly.workers.dev/ " in the "API Endpoint URL" section.
Headers:
- pabbly_api_key: Provide the API key for validation.
- Content-Type: Set to application/json

Sample cURL:

Code:

curl --location 'https://multipartformdata-fileupload.pabbly.workers.dev/' \
--header 'pabbly_api_key: test' \
--header 'Content-Type: application/json' \
--header 'Authorization: <TargetApplicationToken>' \
--data '{
"endpoint": "https://api.targetapp.com/upload",
"file_url": "https://drive.google.com/file/d/1234/view?usp=sharing",
    "headers_to_forward": "authorization",
    "method": "POST",
    "file_key": "profile_photo",
    "body":{
           "file_key": "file"
        }
}'

JSON Body Parameters:

Parameter	Type	Description	Example Value
pabbly_api_key	Header	An authentication key is needed to validate worker access. It should match the predefined key set in the worker code.	pabbly_api_key: {{PabblyPrivateKeyForInternalUse}} NOTE: This key is only used for our internal development for now.
Authorization	Header	Custom header to forward to the target endpoint for further authentication, if required.	Authorization: {{BearerTokenofApplication}}
Content-Type	Header	Defines the content type of the data being uploaded, such as application/json.	Content-Type: application/json
endpoint	JSON Field	Specifies the destination endpoint where the file should be uploaded. Accepts the file path with placeholders for the file name.	"https://target-endpoint.com/api/files/upload/:filename.jpeg"
file_url	JSON Field	URL of the file to be fetched and uploaded to the destination endpoint. The file is downloaded by the worker before being forwarded.	https://imgur.com/knj40OH
file_key	JSON Field	The key name to use for the file in the form data.	File_name
body	JSON Field	An optional set of additional parameters to send in the form data.	{ "user_id": "12345" }
method	JSON Field	Specifies the HTTP method for the request to the destination endpoint. Accepted values are POST, PUT, etc.	"POST"
headers_to_forward	JSON Field	An array of headers is to be forwarded from the initial request to the destination endpoint. Useful for passing tokens or other sensitive information.	["Authorization"]

file_url parameter conditions:

The file_url can be a direct URL. E.g.

https://imgur.com/knj40OH
The file_url can be a direct downloadable drive URL. E.g. https://drive.google.com/uc?export=download&id=1Pn5_9X1JK08t7mw5LR6CnyNes_aAMViy or
https://docs.google.com/spreadsheet...TCfbyoz92Jcl0xyt0cRecM3Ecw/export?format=xlsx
The file_url can be a direct downloadable Dropbox URL. In the case of a normal Dropbox URL, set the value of the ‘dl’ parameter to 1. E.g. https://www.dropbox.com/scl/fi/orsk...ey=4z45zix70yzh5p4sv9cj4f2os&st=2os6wma0&dl=1

Error Handling

The Worker responds with appropriate status codes and messages in case of:

Method not allowed (405): When the request method is not POST.
Unauthorized (401): When the provided API key is incorrect.
Invalid JSON (400): When the request body is not valid JSON.
Missing Required Fields (400): When file_url or endpoint is not provided.
Failed to Fetch File (500): When the Worker cannot retrieve the file from file_url.
Header Not Found (400): When a specified header to forward is missing.

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API to Upload File (multipart/form-data) Documentation​

Overview​

Purpose​

How It Works​

Configuration in Pabbly​

Error Handling​