The third step in setting up your transactional SMS messaging is to trigger an API call to check to see if a contact exists on your short code and transactional list. If the contact does not, follow the Create Contact call to create a new contact. If the contact does exist, but is not subscribed to your transactional list, follow the Subscribe Contact call to update the subscription state of a contact. Be sure to have authenticated yourself before moving to this next step. Follow the below steps to test this in Postman or a REST application of your choice.

1. Open https://api.listrak.com/sms in a tab.
2. Navigate to the Contact tab.
3. Then Get Contact List Collection.
4. Copy the relative Get Contact List Collection URL from the right-hand side of the page.

5. Navigate to Postman.
6. Paste the relative URL in the address bar.
7. Add the List ID associated with your short code from the previous article to the URL.
8. Enter a Phone Number on the end of the URL to check to see if that contact is subscribed.

9. Click Send.

The contact already exists on this list.