I am using the correct live API key.
I have set up the JSON correctly to me and well formatted.
{"engagement":{"active":true,"ownerID":123456789,"type":"NOTE"},"associations":{"contactIds":[123456],"companyIds":[],"dealIds":[],"ownerIds":[]},"meta_data":{"title":"Initial Contact","body":"testing sending to hubspot from test server."}}
I have been into integrations and made sure that all Read from and write to checkboxes are checked.
The scopes look good too.
I get 0 response from the HubSpot server, not even a 4xx response.