ClassNotFoundException when using flink-protobuf with sql-client

sql-client.sh -f protobuf-table.sql -j /protobuf-classes.jar

ADD JAR '/opt/sql-client/lib/flink-sql-connector-kafka-1.16.2.jar';
ADD JAR '/opt/sql-client/lib/flink-protobuf-1.16.2.jar';

SHOW JARS;

CREATE TABLE POSITIONS(id BIGINT) WITH (
      'connector' = 'kafka',
      'format' = 'protobuf',
      'topic' = 'protbuf-topic',
      'properties.bootstrap.servers' = 'kafka:9092',
      'properties.group.id' = 'flink-protobuf',
      'properties.security.protocol' = 'SASL_PLAINTEXT',
      'properties.sasl.mechanism' = 'SCRAM-SHA-512',
      'properties.sasl.jaas.config' = 'org.apache.kafka.common.security.scram.ScramLoginModule required username="user" password="****";',
      'scan.startup.mode' = 'earliest-offset',
      'protobuf.message-class-name' = 'com.example.protobuf.ProtoMessage',
      'protobuf.ignore-parse-errors' = 'true'
      );

SELECT * FROM POSITIONS;

Caused by: java.lang.ClassNotFoundException: com.example.protobuf.ProtoMessage
        at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(Unknown Source)
        at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(Unknown Source)
        at java.base/java.lang.ClassLoader.loadClass(Unknown Source)
        at java.base/java.lang.Class.forName0(Native Method)
        at java.base/java.lang.Class.forName(Unknown Source)
        at org.apache.flink.formats.protobuf.util.PbFormatUtils.getDescriptor(PbFormatUtils.java:89)
        ... 36 more