Sending the user a quick-reply of type
location will pop up a button asking the user to Send Location. If the user selects it then we receive a postback with a payload in this format
Where the two numbers separated by a comma are latitude and longitude co-ordinates in decimal degrees format with the degrees symbols omitted.
Note that the user can move the pin to anywhere in the world before clicking the send button so there is no guarantee that what we receive is the user's true location.