After you've verified that a contact exists and is not subscribed to the list as part of your API call, you may now subscribe a contact to a list.
1. Open api.listrak.com/sms in a new tab.
2. Navigate to Subscribe Contact.
3. Copy the relative Subscribe Contact URL from the right hand side of the page.
4. Navigate to Postman.
5. Paste the relative URL in the address bar.
6. Select POST from the drop-down menu.
7. Enter the Phone Number and Phone List ID in the URL.
8. Click Send.
You've now subscribed a contact to your list.