The "\n" character is not a valid argument separator.

[GhomKrosmonaute]

If you have the following command type :

import * as app from "../app.js"

export default new app.Command({
  name: "hello",
  channelType: "all",
  description: "Say hello to a person",
  positional: [
    {
      name: "firstname",
      description: "First name",
    },
    {
      name: "lastname",
      description: "Last name",
    },
  ],
  async run(message) {
    return message.send(`Hello ${message.args.firstname} ${message.args.lastname}`);
  },
})

Its use could look like !hello Camille Abella and scatter the positionables over several lines should be possible, unfortunately the line breaks are not considered by the Yargs parser as valid argument separators.