Keep running into errors for my workflow

Help me Build my Workflow
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1

I’m trying to send aggregated data from 30 Gong calls to Claude’s API for analysis. My workflow aggregates the calls, builds a prompt, and needs to POST to https://api.anthropic.com/v1/messages.

The Problem: Every approach with the HTTP Request node gives: "JSON parameter needs to be valid JSON"

What I’ve tried:

  1. JSON body with Expression mode - using {{ $json.master_prompt }} in JSON → Error

  2. Using Fields Below - individual parameters for model, max_tokens, messages → Error: “messages: Input should be a valid list”

  3. Pre-built JSON string - created claude_json_body using JSON.stringify() in Edit Fields, then set HTTP Request to “Raw” body with {{ $json.claude_json_body }} → Still same error

  4. Code node - fetch and $http.request() are undefined in sandbox

Current setup (Raw body):

  • Headers: x-api-key, anthropic-version, Content-Type: application/json

  • Body: {{ $json.claude_json_body }} (pre-built JSON string from Edit Fields)

  • Still fails with “JSON parameter needs to be valid JSON”

Environment: n8n 1.110.1 (Self Hosted), HTTP Request node v4.2

Question: How do I send a dynamically built JSON body to an external API? Is there an Anthropic node I should use instead, or a workaround for this validation issue?

2

Instead of using the http node you can try this one.