EliW

var slackTeam = "YOUR_SLACK_TEAM_NAME ";
var token = 'YOUR_ADMIN_TEST_TOKEN'; 
// A test token will suffice.
// You can generate one at https://api.slack.com/docs/oauth-test-tokens
// Just make sure that the user issuing the test token is an admin.

var url = 'https://'+ slackTeam + '.slack.com/api/users.admin.invite';
fetch(url, { 
  method: 'POST',
  headers: {'Content-Type': 'application/x-www-form-urlencoded'},