maven ear configuration for frontend-war and jax-rs-war

i have created a java-ee (jpa/jax-rs2) application packaged as war and a war for html/js frontend. deploying them separately works fine. But i want to create an ear file to package them.

i tried this:

...
<dependencies>
        <dependency>
            <groupId>com.prodyna.pac.moritz</groupId>
            <artifactId>timetracker-backend</artifactId>
            <version>${project.version}</version>
            <type>war</type>
        </dependency>
        <dependency>
            <groupId>com.prodyna.pac.moritz</groupId>
            <artifactId>timetracker-web</artifactId>
            <version>${project.version}</version>
            <type>war</type>
        </dependency>
    </dependencies>
    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-ear-plugin</artifactId>
                <configuration>
                    <finalName>timetracker</finalName>
                    <modules>
                        <webModule>
                            <groupId>com.prodyna.pac.moritz</groupId>
                            <artifactId>timetracker-web</artifactId>
                        </webModule>
                        <webModule>
                            <groupId>com.prodyna.pac.moritz</groupId>
                            <artifactId>timetracker-backend</artifactId>
                        </webModule>
                    </modules>
                </configuration>
            </plugin>
        </plugins>
    </build>
    ...

The problem is: i get many errors about missing dependencies and missing persitence unit. So how to correctly setup ear and war plugins?