Retrieve Plugin Settings and insert into XML string

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>';