n8n - 💡(How to fix) Fix OpenAI credential fails in n8n Cloud: config.headers.setContentType is not a function or OpenAI native credential bug in n8n Cloud 2.19.x 2.20.x 2.21.x

Bug Description

Previously my workspace was on n8n.cloud 2.17.7 and OpenAI nodes were working. After the recent Cloud update, the native OpenAI credential fails with:

config.headers.setContentType is not a function

The same OpenAI API key works via curl and HTTP Request node, so this looks like a regression in the native OpenAI credential.

<img width="1440" height="900" alt="Image" src="https://github.com/user-attachments/assets/d99be0d3-43d0-4a00-bf20-de159c8dedf1" />

To Reproduce

Create new OpenAI credential

Expected behavior

The native OpenAI credential should connect successfully when a valid OpenAI API key is provided.

The same API key works correctly via curl to https://api.openai.com/v1/models and also works inside n8n using an HTTP Request node to https://api.openai.com/v1/responses.

The OpenAI credential test should not fail with config.headers.setContentType is not a function. It should validate the API key and allow the native OpenAI nodes to load models and execute normally.

Debug Info

n8n Cloud workspace: https://synychka2.app.n8n.cloud

n8n version: 2.19.x

Node / credential affected: Native OpenAI credential / OpenAI node

Error message: config.headers.setContentType is not a function

OpenAI credential settings tested: API Key: valid project API key Base URL: https://api.openai.com/v1 Organization ID: empty

What I tested:

1. The same OpenAI API key works via Mac Terminal: curl https://api.openai.com/v1/models -H "Authorization: Bearer $OPENAI_API_KEY"

2. The same OpenAI API key works inside n8n using HTTP Request node: POST https://api.openai.com/v1/responses

3. Only the native OpenAI credential test fails.

Result: This does not look like an OpenAI API key, billing, or quota issue. It looks like a native OpenAI credential regression in n8n Cloud.

Additional note: My workspace previously worked on n8n Cloud 2.17.7. The issue appeared after the Cloud update.

Operating System

mac OS

n8n Version

2.20.X + 2.21.0

Node.js Version

Unknown (n8n Cloud managed environment)

Database

SQLite (default)

Execution mode

main (default)

Hosting

n8n cloud