Trello-Trigger - Bad Request

Hubspot doesn’t use the browser, they trigger webhook requests from their servers iirc, but their webhook logic is special and incredibly frustrating in its very own way (here is one of the mega threads around it). Personally, I’d avoid it all costs and go for a polling approach instead.

CORS headers would typically be configured outside of n8n and are added by a reverse proxy sitting in front of n8n.

While Trello might test the webhook in the browser I don’t think they’d use that in a production environment. After all, there might not be an open browser session when a webhook needs to be sent. So, it might be worth checking with Trello itself what this log output means, and which requirements the target URL has to meet (they could be sending a GET request to verify whether your URL is valid, and then switch to POST requests when actually submitting data, etc.).