Maven: Invalid content was found starting with element 'plugin'

You need to add your code between <plugins> </plugins>

    <build>
      <plugins>
          <plugin>
              <!-- Add here -->
          </plugin>
      </plugins>
    </build>

In case you have multiple plugins, you will add another <plugin> tag under <plugins>.

You have to add the following part in your pom file:

<build>
  <plugins>
      <plugin>
       ...
      </plugin>
  </plugins>
</build>