500 error processed request but returned a blank response

Hi I'm getting this error, and it seems like from the other threads they all got a custom response.

{
"HTTP Status Code": 500,
"message": "The application processed the request but returned a blank response. Refer to the HTTP status code above for details."
}

Here's the information frmo the screenshot so you can easily copy/paste if needed:

Request Headers

Content-Type: application/json
User-Agent: LPS-Webhook/1.0
X-LPS-Api-Key: (if configured)

Payload Format
{
"event": "form_submission",
"form_id": "uuid",
"form_name": "Contact Form",
"project_id": "uuid",
"submission_id": "uuid",
"submitted_at": "2026-03-11T12:00:00Z",
"data": {
"name": "John Doe",
"email": "[email][email hidden][/email]"
}
}
Webhook endpoint did not return the expected X-Validation-Token header. Your endpoint must read the X-Validation-Token from the request header and echo it back in the response header.

Hi @kevind,

Thank you for sharing the details.

Upon checking your workflow, it appears that the source is expecting the headers to be included in the request.

In this case, instead of data forwarder, we recommend using the API by Pabbly module.

Hi,

I've chosen this new API, but im not sure what data or what header im meant to send back

this is what i've put in, but really i have no idea if it's right or wrong

Hi @kevind ,

Thank you for your patience and for sharing the details.

After reviewing your setup, we’d like to inform you that this requirement will not be possible directly within Pabbly Connect. The webhook provider you are using requires a validation step where it sends an X-Validation-Token and expects the same token to be returned in the response headers of the same request.

At the moment, Pabbly Connect does not support modifying or returning custom response headers for webhook triggers, which is why the validation is failing despite your configuration.

To assist you further, could you please share the name of the application/platform from which you have configured this webhook?

We will coordinate with our integration team to check the feasibility of building a native integration for that application, which would help you achieve your use case more smoothly.

Looking forward to your response.