Job for nginx.service failed because the control process exited with error code

Настраивал ssl для сайта на nginx

config:

server {
    listen 443 ssl;
    server_name default_server;
    ssl_certificate /etc/ssl/default_server.crt;
    ssl_certificate_key /etc/ssl/default_server.key;
    location / {

    proxy_pass https://127.0.0.1:6754;
        proxy_set_header Host      $host;
        proxy_set_header X-Real-IP $remote_addr;
    }
}


server {
    listen 80 default_server;

    server_name default_server;

    return 301 https://$host$request_uri;
}


server {
  server_name default_server;
  # [...]
}

ошибка:

Feb 14 16:00:56 urban-bird.vm.hosted-by.adeno.group systemd[1]: Starting A high performance web server and a reverse proxy server...
-- Subject: A start job for unit nginx.service has begun execution
-- Defined-By: systemd
-- Support: https://www.debian.org/support
--
-- A start job for unit nginx.service has begun execution.
--
-- The job identifier is 32245.
Feb 14 16:00:56 urban-bird.vm.hosted-by.adeno.group nginx[471880]: nginx: [emerg] cannot load certificate key "/etc/ssl/default_server.key": PEM_read_bio_PrivateKey() fa>Feb 14 16:00:56 urban-bird.vm.hosted-by.adeno.group nginx[471880]: nginx: configuration file /etc/nginx/nginx.conf test failed
Feb 14 16:00:56 urban-bird.vm.hosted-by.adeno.group systemd[1]: nginx.service: Control process exited, code=exited, status=1/FAILURE
-- Subject: Unit process exited
-- Defined-By: systemd
-- Support: https://www.debian.org/support
--
-- An ExecStartPre= process belonging to unit nginx.service has exited.
--
-- The process' exit code is 'exited' and its exit status is 1.
Feb 14 16:00:56 urban-bird.vm.hosted-by.adeno.group systemd[1]: nginx.service: Failed with result 'exit-code'.
-- Subject: Unit failed
-- Defined-By: systemd
-- Support: https://www.debian.org/support
--
-- The unit nginx.service has entered the 'failed' state with result 'exit-code'.