Katello Agent in DMZ

we have foreman 1.21 in our LAN and a Squid Proxy in our DMZ.
We are using this Proxy to relay all traffic from the DMZ to our LAN.
Now we have a problem with the Clients installed with Foreman, which are running the katello agent, to get a connect to the foreman server.
I have already configured the proxy in /etc/yum.conf, which is working fine, and in /etc/rhsm/rhsm.conf
I’m still getting error messages ifrom goferd:
[ERROR][worker-0] gofer.messaging.adapter.connect:33 - connect: proton+amqps://:5647, failed: Connection amqps://:5647 disconnected: Condition(‘proton:io’, ‘recv: errno: 111’)
Port 5647 is working from the proxy server to the foreman server in our LAN
Expected outcome:
no error messages
Foreman and Proxy versions:
Foreman 1.21.3
Katello 3.11.1
Foreman and Proxy plugin versions:

Other relevant data:
[e.g. logs from Foreman and/or the Proxy, modified templates, commands issued, etc]
(for logs, surround with three back-ticks to get proper formatting, e.g.)