topic Issues with the new Developper platform (CORS?) in APIs & Integrations

Issues with the new Developper platform (CORS?)

PAtlan — Fri, 03 Oct 2025 16:58:15 GMT

I'm trying to run an MCP server to access HubSpot from Mistral.ai.

I've been following this guide https://developers.hubspot.com/docs/apps/developer-platform/build-apps/integrate-with-hubspot-mcp-server

In order to create an App on the new platform as requested, I've followed this guide:

https://developers.hubspot.com/docs/getting-started/quickstart

I've managed to set up a developper account, and I've managed to upload a get-started project and add the card to the central column.

Unfortunately I get an error message in the card:

and if I look into the developper console i see the following message:

I am located in Europe, so I'm assuming the template used to build the app uses a standard origin url (https://app.hubspot.com) instead of the one my developper platform is running on (https://app-eu1.hubspot.com) .

I'm assuming this is a CORS issue, but I have no knowledge at all of how to solve it.

As anyone faced a similar issue or know how to solve it?

Thanks !

Re: Issues with the new Developper platform (CORS?)

STierney — Fri, 03 Oct 2025 18:13:13 GMT

Hey @PAtlan - thanks for posting in the Community!

I'd like to tag in some experts here to see if they have any insight for us! @mangelet, @HubDoPete, and @miljkovicmisa - any idea what may be causing this error?

Shane, Senior Community Moderator

Re: Issues with the new Developper platform (CORS?)

FaramarKolivand — Mon, 06 Oct 2025 12:29:57 GMT

Err_Blocked_By_Client means your own browser (typically an extension in your browser, maybe adblocker?) blocked the request, but that's not the main issue here. Check the component name in your extension.json project and make sure it is matching with the component exported bt your bundle.