Can you include the xml namespace portions at the top of your changelog.xml and dbchangelog-ext.xsd file? The error you are running into may be due to that format. The vacuum prefix namespace may not be defined.
Also, I ran into a similar issue with running the liquibase jar from command line. --classpath will not pick up your custom jar. Instead do the following pass the jars on the classpath jvm option and only pass in your db driver jar on --classpath. Similar to below:
java -cp lib/liquibase-custom.jar;liquibase.jar;lib/postgresql-42.1.4.jar liquibase.integration.commandline.Main --driver=org.postgresql.Driver --classpath=lib/postgresql-42.1.4.jar --changeLogFile=sdk/workspace/changelog/com/example/changelog.xml --url="jdbc:postgresql://localhost:5432/Demo1" --username=postgres --password=1234 update
Also, I ran into a similar issue with running the liquibase jar from command line. --classpath will not pick up your custom jar. Instead do the following pass the jars on the classpath jvm option and only pass in your db driver jar on --classpath. Similar to below:
java -cp lib/liquibase-custom.jar;liquibase.jar;lib/postgresql-42.1.4.jar liquibase.integration.commandline.Main --driver=org.postgresql.Driver --classpath=lib/postgresql-42.1.4.jar --changeLogFile=sdk/workspace/changelog/com/example/changelog.xml --url="jdbc:postgresql://localhost:5432/Demo1" --username=postgres --password=1234 update