Admin login fails with 401

thanks @sunnyson, my config/server.js is:

module.exports = ({ env }) => ({
  host: env('HOST', '0.0.0.0'),
  port: env.int('PORT', 1337),
  url: 'https://customurl.com/api',
  admin: {
    auth: {
      secret: env('ADMIN_JWT_SECRET', '1e978b20a8532605b42d18bf01ea37f4'),
    },
  },
});

I too tried to use: {secret: ‘1e978b20a8532605b42d18bf01ea37f4’,}, not works

and nginx conf is:

    # Strapi API and Admin
    location /api/ {
        rewrite ^/api/(.*)$ /$1 break;
        proxy_pass http://strapi;   // upstream has been set to http://127.0.0.1:1337
        proxy_http_version 1.1;
        proxy_set_header X-Forwarded-Host $host;
        proxy_set_header X-Forwarded-Server $host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Proto $scheme;
        proxy_set_header Host $http_host;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection "Upgrade";
        proxy_pass_request_headers on;
    }