sshkeys (ciuser) to an VM endpoint (format error)

[iamralf]

I receive following error from the Proxmox-API (v8.1.10):

{"sshkeys": "invalid format - invalid urlencoded string: ssh-rsa%20AA.................................%20eom\n"}}, "msg": "Status code was 400 and not [200]: HTTP Error 400: Parameter verification failed.", "pragma": "no-cache", "redirected": false, "server": "pve-api-daemon/3.0", "status": 400, "url": "https://proxmox:8006/api2/json/nodes/cluster01/qemu/5000/config"}

The same issue seems to be reported here, but the solution is not applicable. Sorry for posting there, but without response:
https://forum.proxmox.com/threads/sshkeys-invalid-format-invalid-urlencoded-string.126202/

{{ | urlencode }} does its job in the Ansible task (There are no "\n" or "+").
However, "\n" is appended to the content of the sshkey-variable in the error message back from the Proxmox server.
The code runs without the sshkeys line in the Ansible task below. ("ciuser" and "cipassword").

My Ansible task look like:

   - name: configure vm
     uri:
       url: "https://{{ server_url }}:8006/api2/json/nodes/{{ node }}/qemu/{{ vmid_next | trim }}/config"
       method: POST
       return_content: yes
       body_format: json
       use_proxy: no
       validate_certs: no
       timeout: 5
       headers:
         Authorization: "PVEAPIToken=..."
         Content-Type: "application/json"
       body:
         [...]
         ciuser: "{{ inventory_settings__pve_vm_username }}"
         sshkeys: "{{ inventory_settings__pve_vm_public_key | trim | urlencode }}"
     [...]

What is the problem here? Thanks for any help!