docker reverse nginx proxy with letsencrypt keeps on printing erros: 'can not init api'

I have docker-compose file that is executed on a raspberry pi within my home network. My pi's ipv6 address with port 443 and 80 is exposed to the internet and also reachable. My provider does not give me a static ipv4 address and due to my hardware I can only expose a ipv6 hosts.

In the docker-compose.yaml I leverage https://hub.docker.com/r/jwilder/nginx-proxy with theletsencrypt-nginx-proxy-companion.

version: '3'

services:
  proxy:
    image: jwilder/nginx-proxy:alpine
    labels:
      - 'com.github.jrcs.letsencrypt_nginx_proxy_companion.nginx_proxy=true'
    container_name: proxy
    networks:
      - raspberry_network
    ports:
      - 80:80
      - 443:443
    environment:
      - ENABLE_IPV6=true
    volumes:
      - ./proxy/conf.d:/etc/nginx/conf.d:rw
      - ./proxy/vhost.d:/etc/nginx/vhost.d:rw
      - ./proxy/html:/usr/share/nginx/html:rw
      - ./proxy/certs:/etc/nginx/certs:ro
      - /etc/localtime:/etc/localtime:ro
      - /var/run/docker.sock:/tmp/docker.sock:ro
    restart: always

  letsencrypt:
    image: jrcs/letsencrypt-nginx-proxy-companion
    container_name: letsencrypt
    depends_on:
      - proxy
    networks:
      - raspberry_network
    volumes:
      - ./proxy/certs:/etc/nginx/certs:rw
      - ./proxy/vhost.d:/etc/nginx/vhost.d:rw
      - ./proxy/html:/usr/share/nginx/html:rw
      - /etc/localtime:/etc/localtime:ro
      - /var/run/docker.sock:/var/run/docker.sock:ro
    restart: always


networks:
  raspberry_network:

However, I keep on receiving that message in the logs:

letsencrypt    | 2021/04/29 22:35:26 Debounce minTimer fired
letsencrypt    | 2021/04/29 22:35:27 Generated '/app/letsencrypt_service_data' from 5 containers
letsencrypt    | 2021/04/29 22:35:27 Running '/app/signal_le_service'
letsencrypt    | [Thu Jan  1 01:00:00 CET 1970] Please refer to https://curl.haxx.se/libcurl/c/libcurl-errors.html for error code: 6
letsencrypt    | [Thu Jan  1 01:00:00 CET 1970] Can not init api.
letsencrypt    | [Thu Jan  1 01:00:00 CET 1970] Registering account: https://acme-v02.api.letsencrypt.org/directory
letsencrypt    | [Thu Jan  1 01:00:00 CET 1970] Please refer to https://curl.haxx.se/libcurl/c/libcurl-errors.html for error code: 6
letsencrypt    | [Thu Jan  1 01:00:00 CET 1970] Could not get nonce, let's try again.