Can't reach Cloud Connector through IDoc Adapter

Hello Experts,

I'm trying to send an IDoc to my ECC. I'm using a Cloud Connector.

The Cloud Connector is connected to the Cloud Platform. I'm able to ping the Cloud Connector with the Connectivity Test within the CPI Tenant. Anyway when I'm trying to get a connection through an iFlow I'm getting errors.

What I've tried:

Proxy Type Internet, On-Premise and https/http in Address.

I'm always getting an UnknownHostException or HTTP 400. Any Idea?

Best Regards

René