Email template modification

./config/server.js

module.exports = ({ env }) => ({
    host: env("HOST", "0.0.0.0"),
    port: env.int("PORT", 1337),
    admin: {
      auth: {
        secret: env('ADMIN_JWT_SECRET', process.env.ADMIN_JWT_SECRET),
      },
    },
  });

./config/env/production/server.js

module.exports = ({ env }) => ({
    host: env("HOST", process.env.HOST || "0.0.0.0" ),
    port: env.int("PORT", process.env.PORT || 4000),
    admin: {
      auth: {
        secret: env('ADMIN_JWT_SECRET', process.env.ADMIN_JWT_SECRET),
      },
    },
  });

I use heroku to deploy my app, if I use “myapp.herokuapp.com” as host variable i got an error.
Do you know where could I find the informations of HOST and PORT ?

and my email config provider : config/plugins.js

module.exports = ({ env }) => ({
    email: {
      provider: 'sendgrid',
      providerOptions: {
        apiKey: env('SENDGRID_API_KEY', process.env.SENDGRID_API_KEY),
      },
      settings: {
        defaultFrom: 'hello@test.com',
        defaultReplyTo: 'hello@test.com',
      },
    },
  });