CallFire Tech Lead Pete says:The extra data field is populated when an array of phone numbers is entered via a web service call:
example:
Assume you are using the function call : "createBroadcastWithTransfer" The numbers object is an Array of String type
in order to include extra data an element in the array would be:
numbers[0]=<phonenumber>,<account-number>
or more literally:
numbers[0]=2135552255,67Y677858&4535
The extra data field would be populated with: "67Y677858&4535"
