Nginx in docker does not see the certificate files

Expected behavior

Site to be served via https

Actual behavior

Site does not get served at all.
Docker compose logs for nginx container return:

nginx: [emerg] cannot load certificate "/etc/nginx/certs/fullchain1.pem": BIO_new_file() failed (SSL: error:80000002:system library::No such file or directory:calling fopen(/etc/nginx/certs/fullchain1.pem, r) error:10000080:BIO routines::no such file)

Additional Information

The nginx configuration is as follows:

events {
    
}

http {
    server {
    listen 80;
    listen [::]:80;

    server_name my-reducted-domain.com www.my-reducted-domain.com;
    server_tokens off;

        location / {
            proxy_pass http://flask:56733;
            proxy_set_header Host $host;
            proxy_set_header X-Real-IP $remote_addr;
            # Additional proxy settings if needed...
        }
    }
    server {
    listen 443 ssl;
    server_name my-reducted-domain.com;
        ssl_certificate /etc/nginx/certs/fullchain1.pem;
        ssl_certificate_key /etc/nginx/certs/privkey1.pem;
    client_max_body_size 20M;
    index index.html;
        location / {
                proxy_pass http://my-reducted-domain.com;
        }
    }
}

The docker-compose.yml relelvant service is:

  nginx:
    image: nginx:alpine
    container_name: spun-flask-nginx
    restart: unless-stopped
    ports:
      - 80:80
    volumes:
      - ./nginx.conf:/etc/nginx/nginx.conf:ro
      - ./certs:/etc/nginx/certs  
    networks:
      - flask

The directory certs has inside:

myuser@spun-test-8-nginx-docker-compose:/var/lib/myproject$ ls -l certs
total 24
-rw-r--r-- 1 myuser docker   66 Nov 23 11:54 README
-rw-r--r-- 1 myuser docker 1497 Nov 23 12:40 cert1.pem
-rw-r--r-- 1 myuser docker 3749 Nov 23 12:40 chain1.pem
-rw-r--r-- 1 myuser docker 5246 Nov 23 12:39 fullchain1.pem
-rw------- 1 myuser docker  241 Nov 23 12:40 privkey1.pem

When I do an ls from inside the nginx container I see the files being there:

myuser@spun-test-8-nginx-docker-compose:/var/lib/myproject$ docker-compose run --rm nginx ls -l /etc/nginx/certs/
total 24
-rw-r--r--    1 1001     997             66 Nov 23 11:54 README
-rw-r--r--    1 1001     997           1497 Nov 23 12:40 cert1.pem
-rw-r--r--    1 1001     997           3749 Nov 23 12:40 chain1.pem
-rw-r--r--    1 1001     997           5246 Nov 23 12:39 fullchain1.pem
-rw-------    1 1001     997            241 Nov 23 12:40 privkey1.pem

As a test (only a test) I tried changing ownership or permissions of the files, and always get the same error:

cannot load certificate "/etc/nginx/certs/fullchain1.pem"

Any ideas what else to try?