php 따음표 안에 함수 넣기 질문입니다.

<?php

$data = '{

        "Messages":[

{

                "From": {

                    "Email": ". $fmail .",

                    "Name": ". $fname ."

                },

                "To": [

                 {

                     "Email": ". $to ."

                    }

                ],

                "Subject": "Your email flight plan!",

                "HTMLPart": "<h3>Dear passenger 1, welcome to Mailjet!</h3><br/>May the delivery force be with you!"

            }

        ]

    }';

?>