Attempts to find and return a contact using the email address or mobile number. If a contact is not found, a new contact is created.
This API is similar to the Get a Contact API, but creates a new contact if a contact is not found.
Find or create by email address /api/v1/contact/upsert?email=ben@example.com
Find or create by mobile phone /api/v1/contact/upsert?mobilephone=+155512345678