Hubspot MCP server <> n8n - Bad Client ID

[Simpson007]

Hey guys,

I’m kind of stuck as neither Gemini nor Claude can help me solve this.

I am trying to use the Hubspot MCP server node with the MCP OAuth2 API inside n8n with the following settings:

Grant Type	PKCE
Authorization URL	https://mcp.hubspot.com/oauth/authorize
Access Token URL	https://api.hubapi.com/oauth/v1/token
Client ID	Hubspot ID
Client Secret	Hubspot MCP App Secret
Scope	oauth
Authentication	Send credentials in Body
Auth URI Query Parameters	Leave empty

Once i try to connect the app, choose my account and enable different permission scopes i finally retrieve this error.

Anyone knows how to solve this?

THANKS!

Runnning the n8n instance on 2.2.3 via Hostinger VPS.

[Miliaga]

@Simpson007 so hubspot’s standard OAuth2 flow doesn’t use PKCE (Proof Key for Code Exchange) by default, and the authorization URL you’re using appears to be for HubSpot’s MCP (Marketing Contacts Platform) which has different requirements.

[Simpson007]

@Simpson007

https://api.hubapi.com/oauth/v1/token

@Miliaga Thanks for the reply.

I swapped to “Authorization Code” as Grant Type and tried different URLs.

Getting another error this time. Can you help us out and maybe test this on your side here?

n8n docs for this unfortunately lead to a404 blank page.
Much appreciated.

[Miliaga]

@Simpson007

Update your URLs to:

Authorization URL: https://app.hubspot.com/oauth/authorize

Access Token URL: https://api.hubapi.com/oauth/v1/token

[zatech2023-rgb]

Hi
The error you’re seeing is due to HubSpot MCP OAuth flow limitations, not n8n.
Key points:
PKCE grant type is not fully supported by HubSpot MCP.
The authorization succeeds, but token exchange fails.
oauth alone is not a valid scope — HubSpot requires specific scopes like crm.objects.contacts.read.
Solutions:
Use standard HubSpot OAuth (Authorization Code grant)
Auth URL: https://app.hubspot.com/oauth/authorize
Token URL: https://api.hubapi.com/oauth/v1/token
Define proper scopes
Redirect URI must match n8n exactly
Use MCP via Private App / Bearer Token
Create a private app in HubSpot
Use HTTP Request node in n8n instead of OAuth
Bypasses PKCE limitations

[Simpson007]

Thanks guys. Adjusted the URLs and now I get this error message:

”Error: Insufficient parameters for OAuth2 callback.

More details

Received following query parameters: {"error":"invalid_request","error_description":"Missing or unknown code challenge","

Any ideas?

//Claude tells me this:
The issue is tracked here: GitHub Issue #22103

[JohnHalex]

Hi @Simpson007 ,

Instead of using the generic OAuth2 API credential, look for “HubSpot” in the credentials list this should work without these OAuth issues.

And the GitHub issue is being tracked, but no ETA on a fix yet.

[Simpson007]

nope, does not work.

seems like i go back to classic work and just add different API endpoint calls as tools attached to an agent…