You don’t need the echo
when you are concatenating strings. Just remove it.
$xmlInputData="<?xml version="1.0" encoding="utf-8" ?><data><settings><origin="".
$my_options['origin'] .'" username="'.
$my_options['user'] . '" password="'.
$my_options['password'] . '" /></settings><enquiries><lead productName=\"Appointment Booking"><customer><name>'.
$_REQUEST['first-name'].' '.
$_REQUEST['last-name'].'</name><email>'.
$_REQUEST['email'].'</email><postcode>'.
$_REQUEST['postal'].'</postcode><houseNumber></houseNumber><address></address><city></city><region></region><tel>'.
$_REQUEST['phone-number'].'</tel><mobile></mobile><notes></notes></customer></lead></enquiries></data>';