Dependency Version is missing - 'dependencies.dependency.version' for io.vertx:vertx-stack-depchain:jar is missing

Trying to specify my vertx version for different modules in the parent pom.
My parent pom file is:

<groupId>com.abc.xyc</groupId>
<artifactId>parent</artifactId>
<version>1.0-SNAPSHOT</version>
<packaging>pom</packaging>
<name>Parent POM</name>

<modules>
    ...
    <module>Server</module>
    ...
</modules>

<properties>
    ...
    <vertx.version>3.8.2</vertx.version>
    <vertx.verticle>com.abc.xyc.as4.MainVerticle</vertx.verticle>
    <vertx-maven-plugin.version>1.0.22</vertx-maven-plugin.version>
    <lmax.version>3.4.2</lmax.version>
    ...
</properties>

<dependencyManagement>
    <dependencies>
        ...
        <dependency>
            <groupId>io.vertx</groupId>
            <artifactId>vertx-stack-depchain</artifactId>
            <version>${vertx.version}</version>
            <type>pom</type>
            <scope>import</scope>
        </dependency>
        <dependency>
            <groupId>io.vertx</groupId>
            <artifactId>vertx-core</artifactId>
            <version>${vertx.version}</version>
        </dependency>
        ...
    </dependencies>
</dependencyManagement>

<build>
        <pluginManagement>
            ...
            <plugins>
                <plugin>
                    <groupId>io.reactiverse</groupId>
                    <artifactId>vertx-maven-plugin</artifactId>
                    <version>${vertx-maven-plugin.version}</version>
                    <executions>
                        <execution>
                            <id>vmp</id>
                            <goals>
                                <goal>initialize</goal>
                                <goal>package</goal>
                            </goals>
                        </execution>
                    </executions>
                    <configuration>
                        <redeploy>true</redeploy>
                    </configuration>
                </plugin>
            </plugins>
        </pluginManageme>
</build>

This is my child pom file

<artifactId>Server</artifactId>
<version>1.0-SNAPSHOT</version>
<packaging>jar</packaging>

<parent>
    <groupId>com.abc.xyc</groupId>
    <artifactId>parent</artifactId>
    <version>1.0-SNAPSHOT</version>
</parent>

<dependencies>
    ...
    <dependency>
        <groupId>io.vertx</groupId>
        <artifactId>vertx-stack-depchain</artifactId>
    </dependency>
    ... 
</dependencies>

The error I get is:'dependencies.dependency.version' for io.vertx:vertx-stack-depchain:jar is missing. When I specify the version in child pom, it works fine. My question is why isn't it getting the version from my parent pom?

It's because it does not "manage" its own version, it manages other dependencies via <dependencyManagement>.

In general, there is no need to import the vertx-stack-depchain as a depenedency, it should be a parent or like you did in dependency-management with <scope>import</scope> and then you can do things like the following in your child poms:

<dependency>
    <groupId>io.vertx</groupId>
    <artifactId>vertx-core</artifactId>
</dependency>

If you still find a good reason to import the dep-chain itself, then you need to specify the version.