Help Needed: Persistent "Bad Request" Error with n8n HTTP Request Node and Vapi API

[Zarim]

Hi everyone,

I’m new to n8n and I’m working on a project for an assignment. I’m trying to build an outbound AI lead qualification agent, but I’m completely stuck on an error and my deadline is approaching. I would be extremely grateful for any guidance.

My Project Goal: The workflow should:

1. Trigger when a new row is added to a Google Sheet (containing a lead’s name and phone number).

2. Use the HTTP Request node to send an API call to Vapi (on a free trial) to initiate a phone call to that lead.

3. The Vapi AI agent then qualifies the lead.

The Problem: The Google Sheets trigger works perfectly and pulls the data. However, the HTTP Request node consistently fails with the error: Problem in node 'HTTP Request' - Bad request - please check your parameters.

My HTTP Request Node Setup:

• Method: POST

• URL: https://api.vapi.ai/call/phone

• Authentication: Generic Credential Type → Header Auth

  • Credential Name: Authorization

  • Credential Value: Bearer [MY_VAPI_API_KEY]

• Send Body: Toggled ON

• Body Content Type: JSON

• Specify Body: json

• JSON Body Code:

  JSON

  {
    "assistantId": "[MY_VAPI_ASSISTANT_ID]",
    "customer": {
      "number": "{{ $json['Phone Number'] }}"
    }
  }
  
  

What I’ve Already Tried: I feel like I’ve tried everything, including:

• Generating a brand new Private API Key from Vapi and creating a new credential in n8n.

• Confirming the assistantId is copied correctly from the Vapi URL and pasted in the JSON.

• Using a valid US-based phone number (from TextNow) in the Google Sheet to avoid free trial limitations. The number is in the correct +1... format.

• Confirming my Google Sheet column is named exactly Phone Number.

• Deleting and recreating the HTTP Request node from scratch.

I’ve been stuck on this for several days. If anyone can spot a mistake in my setup described above, I would really appreciate the help.

Thank you in advance!

[c0d33ngr]

Hi @Zarim I don’t think Vapi API can call international phone numbers with free trial. I seems it’ has to be US phone numbers.

I did make an HTTP Request to the APi to call but got 400 status code error

[Zarim]

Thank you so much for helping, but I’m using US number and same error occurs. @c0d33ngr

[c0d33ngr]

@Zarim Oh.. I see.
I did try it out with a friend US phone number and it HTTP Request node seem to send the request.

[c0d33ngr]

I think it’s your json sttucture - It’s not complete, no phoneNumberId

[Zarim]

@c0d33ngr still not working,

[c0d33ngr]

@Zarim This basic workflow above, make a request to Vapi API. You should try make a single request using the workflow

Also, it would helps if you share some visuals from your end - like the exact error messages, nodes or something to assist

[Zarim]

@c0d33ngr bro is there any way we can discuss this on call or something like?

[c0d33ngr]

@Zarim Your endpoint is wrong. It’s https://api.vapi.ai/call NOT https://api.vapi.ai/call/phone

Here’s quickstart guide from Vapi API documentation Phone calls | Vapi

You can also send me private DM too via [email protected]