Problems with Opnsense / Letsencrypt-ACME / sftp


I would like to upload the certificates I created with opnSense to my home assistant using sftp.

As far as I can see, there are two ways to do this:
a) Upload via sftp
b) Upload via ssh script

Unfortunately I can’t get that far because I can’t establish a connection with the homeassistant ssh/sftp.
I fail because a host key is required…

I’m using SSH & Web Terminal, and this is what my configuration looks like:

allow_agent_forwarding: true
allow_remote_port_forwarding: true
allow_tcp_forwarding: true
authorized_keys: []
compatibility_mode: false
password: mypassword
sftp: true
username: root

But how?
Does anyone have instructions on how to do this?