Reject Error

[sup-Udh]

The Error-

[
  {
    email: '[email protected]',
    status: 'rejected',
    _id: 'eb31ad9effcf4c0084484496fe3eff2d',
    reject_reason: 'unsigned'
  }
]

the code-

const mailchimp = require("@mailchimp/mailchimp_transactional")(
    "HIDDEN API KEY",
  );
 export default function test(){

    const message = {
        from_email: "[email protected]",
        subject: "Hello world",
        text: "Welcome to Mailchimp Transactional!",
        to: [
          {
            email: "[email protected]",
            type: "to"
          }
        ]
      };
      
      async function run() {
        const response = await mailchimp.messages.send({
          message
        });
        console.log(response);
      }
      run();

 }

does anyone know why this happens?