In general, 3rd party services are responsible for supporting their service/app/integration. If they believe the issue is with HubSpot, I’d be happy to help troubleshoot. I’ll need more details on what’s going wrong. If they’re getting a 204 response from the form submission endpoint, that would lead me to believe everything is working correctly.
Would help if you were able to provide the information on what and how the service does what it does. The response you get is in fact success. HubSpot API returns 204 No Content when there is no error and everything went well.
Also if someone provides you a service that operates with HubSpot, they should be the ones figuring out why their product doesn’t work
Are you trying to access the API with AJAX?
If that is the case, join the club
Hubspot blocks all AJAX requests to the API.
You will have to setup another server with an API which in turn makes the calls to the hubspot API.
The reason it worked before is because there was a bug which allowed hubspot generated domains to access the API.