Ansible callback with letsencrypt

when using the ansible callback module I get the following error message:

[WARNING]: Sending data to Foreman at https://foreman.home failed for HTTPSConnectionPool(host='foreman.home', port=443): Max retries exceeded with
url: /api/v2/hosts/facts (Caused by SSLError(SSLError(1, '[SSL: TLSV1_ALERT_UNKNOWN_CA] tlsv1 alert unknown ca (_ssl.c:2622)')))

I used the following command to setup the certificates in foreman (linebreaks for better readability):

foreman-installer --foreman-server-ssl-cert /etc/letsencrypt/live/foreman.home/cert.pem 
--foreman-server-ssl-chain /etc/letsencrypt/live/foreman.home/chain.pem 
--foreman-server-ssl-key /etc/letsencrypt/live/foreman.home/privkey.pem 
--foreman-proxy-foreman-ssl-ca /etc/ssl/certs/ca-certificates.crt 
--puppet-server-foreman-ssl-ca /etc/ssl/certs/ca-certificates.crt

This is my ansible.cfg:

callback_whitelist = foreman

url = 'https://foreman.home'
ssl_cert = /etc/letsencrypt/live/foreman.home/cert.pem
ssl_key = /etc/letsencrypt/live/foreman.home/privkey.pem
ssl_ca = /etc/letsencrypt/live/foreman.home/fullchain.pem
verify_certs = 0

The cert got applied successfully to the web-ui, but when I tried to debug the issue, it looks like foreman-proxy is using a different certificate, is this correct? Do I maybe need to setup the certificates different?

Here is some more information, because I just cannot get this to work:

My host environment is Debian 11 VM on Proxmox. 2 Cores 8 Gb RAM. Foreman Version is Version 3.7.0-develop (When you follow the quickstart on the homepage for 3.6 the description is actually for 3.7 nightly → Foreman :: Quickstart).
I get my certificates from labca which is using boulder acme.