In the request of the booking by reference you can search for the booking data through the booking reference. Within the tag filters -> filter type you can specify the parameter of your search:

• type reference + code retrieves the data of the specified booking code.

<envelope>
    <header>
        <actor> test</actor>
        <user>test</user>
        <password>test</password>
        <version>1.0.0</version>
        <timestamp>20200501170000</timestamp>
    </header>
    <query type="track" product="bookings">
        <filters>
            <filter type="reference" code=""/>
        </filters>
    </query>
</envelope>