Create an opt-out
Opts a number out so messages are no longer sent to it. The number is added to your default
opt-out list unless you pass opt_out_list_id or opt_out_list_name (not both). A list
named by opt_out_list_name is created if it does not exist. If the number is already opted
out, the existing opt-out is returned.
POST
https://app.touchsms.com.au/api/v2/optouts