Add metadata to Rollbar log appender in Spring Boot

Question

How can I add metadata or custom fields to an XML based Logback configuration in a Spring Boot project so that they are visible in Rollbar's web ui?

This is what I have added to the logback-spring.xml file:

<springProfile name="logging-profile">
    <springProperty scope="context" name="rollbar.api-key" source="rollbar.api-key"/>
    <springProperty scope="context" name="rollbar.enabled" source="rollbar.enabled"/>
    <springProperty scope="context" name="rollbar.level" source="rollbar.level" default="ERROR"/>
    <springProperty scope="context" name="host" source="host"/>
    <springProperty scope="context" name="environment" source="environment"/>
    <springProperty scope="context" name="region" source="region"/>

    <appender name="rollbar-sync" class="com.rollbar.logback.RollbarAppender">
        <accessToken>${rollbar.api-key}</accessToken>
        <codeVersion>@git.commit.id@</codeVersion>
        <enabled>${rollbar.enabled}</enabled>
        <environment>${environment}</environment>
        <framework>spring-boot</framework>
        <level>${rollbar.level}</level>
        <language>java</language>
        <server>
            <host>${host}</host>
            <metadata>
                <env>${environment}</env>
                <region>${region}</region>
                <version>@project.version@</version>
            </metadata>
        </server>
    </appender>
</springProfile>

When running the service I see related log entries in the Rollbar web ui, however the fields defined in the <metadata> section are missing. Consequently, I suspect