Configuring multiple nginx serverblocks to serve multiple domains with a django app

I have a perfectly working nginx configuration that serves a django app which looks like this:

server {

    listen 443 ssl;
    server_name domain.de;
    proxy_max_temp_file_size 0;
    proxy_buffering off;
    charset utf-8;
    ssl_stapling off;
    ssl_stapling_verify off;

    ssl_certificate            /etc/letsencrypt/live/domain.de/fullchain.pem;
    ssl_certificate_key       /etc/letsencrypt/live/domain.de/privkey.pem;


    set $my_host $http_host;
    if ($http_host = "domain.de") {
          set $my_host "domain.de";
    }


    location / {
        proxy_pass http://django:5000;
        proxy_set_header Host $my_host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    }

}

server {
        listen 80 ;
        server_name domain.de;
        return 301 https://domain.de$request_uri;
}
server {
        listen 80 ;
        server_name www.domain.de;
        return 301 https://domain.de$request_uri;
}
server {
        listen 443 ;
        server_name www.domain.de;
        return 301 https://domain.de$request_uri;
        ssl_stapling off;
        ssl_stapling_verify off;

        ssl_certificate           /etc/letsencrypt/live/domain.de/fullchain.pem;
        ssl_certificate_key       /etc/letsencrypt/live/domain.de/privkey.pem;
}

What I want to do is to add a new domain (let's say domain.com). I already got the certificates. No matter how I add another serverblock I get a 400 response telling me that the certificate is not valid.

EDIT: I am running nginx in a docker-container:

nginx:
    container_name: 'nginx'
    image: nginx:latest
    ports:
      - "80:80"
      - "443:443"
    volumes: ##The following files are found on the linux server.
       - /root/nginx-conf/hbe.conf:/etc/nginx/conf.d/default.conf
       - /root/nginx-conf/main.conf:/etc/nginx/nginx.conf
       - /etc/letsencrypt/live/domain.de/fullchain.pem:/etc/letsencrypt/live/domain.de/fullchain.pem
       - /etc/letsencrypt/live/domain.de/privkey.pem:/etc/letsencrypt/live/domain.de/privkey.pem
       - /etc/letsencrypt/live/domain.com/fullchain.pem:/etc/letsencrypt/live/domain.com/fullchain.pem
       - /etc/letsencrypt/live/domain.com/privkey.pem:/etc/letsencrypt/live/domain.com/privkey.pem
    depends_on:
      - django

I tried or example to copy the main server-block adjusting the domain-name and the certificate location:

server {

    listen 443 ssl;
    server_name domain.de;
    proxy_max_temp_file_size 0;
    proxy_buffering off;
    charset utf-8;
    ssl_stapling off;
    ssl_stapling_verify off;

    ssl_certificate            /etc/letsencrypt/live/domain.de/fullchain.pem;
    ssl_certificate_key       /etc/letsencrypt/live/domain.de/privkey.pem;


    set $my_host $http_host;
    if ($http_host = "domain.de") {
          set $my_host "domain.de";
    }


    location / {
        proxy_pass http://django:5000;
        proxy_set_header Host $my_host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    }

}

server {

    listen 443 ssl;
    server_name domain.com;
    proxy_max_temp_file_size 0;
    proxy_buffering off;
    charset utf-8;
    ssl_stapling off;
    ssl_stapling_verify off;

    ssl_certificate            /etc/letsencrypt/live/domain.com/fullchain.pem;
    ssl_certificate_key       /etc/letsencrypt/live/domain.com/privkey.pem;


    set $my_host $http_host;
    if ($http_host = "domain.com") {
          set $my_host "domain.com";
    }


    location / {
        proxy_pass http://django:5000;
        proxy_set_header Host $my_host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    }

}

I also tried copying the rest of the server blocks, adjusting the URL, but no matter how I do it, I still get a 400 bad request.

I'm really not an expert with nginx, would be very grateful if someone could lend me a hand. Thanks so much in advance!