const SiteClient = require('datocms-client').SiteClient;
const client = new SiteClient('YOUR-API-TOKEN');
client.maintenanceMode.activate({
  force: true
})
.then((maintenanceMode) => {
  console.log(maintenanceMode);
})
.catch((error) => {
  console.error(error);
});

> node example.js
{
  "id": "4235",
  "active": false
}