Kafka Connect protobuf converter not found

I have a kafka s3-sink connector which I'm producing messages to. However when I send messages to the topic, I'm noticied the logs of my sink connector are throwing me this error:

│ Invalid value io.confluent.connect.protobuf.ProtobufConverter for configuration value.converter: Class io.confluent.connect.protobuf.ProtobufConverter could not be found.  

Here's my sink:

apiVersion: kafka.strimzi.io/v1beta2
kind: KafkaConnector
metadata:
  name: test-s3-sink
  labels:
    # The strimzi.io/cluster label identifies the KafkaConnect instance
    # in which to create this connector. That KafkaConnect instance
    # must have the strimzi.io/use-connector-resources annotation
    # set to true.
    strimzi.io/cluster: test-cluster
spec:
  class: io.confluent.connect.s3.S3SinkConnector
  tasksMax: 6
  config:
    name: test-s3-sink
    topics: testing-stack-overflow-topic
    flush.size: 100
    s3.bucket.name: test-bucket
    s3.region: us-east-1
    storage.class: io.confluent.connect.s3.storage.S3Storage
    format.class: io.confluent.connect.s3.format.avro.AvroFormat
    store.kafka.keys: true
    keys.format.class: io.confluent.connect.s3.format.avro.AvroFormat
    key.converter: "io.confluent.connect.protobuf.ProtobufConverter"
    key.converter.schema.registry.url: "http://localhost:8081"
    key.converter.schemas.enable: true
    value.converter: "io.confluent.connect.protobuf.ProtobufConverter"
    value.converter.schema.registry.url: "http://localhost:8081"
    value.converter.schemas.enable: true
    rotate.interval.ms: 3600000
    timezone: UTC
    behavior.on.null.values: ignore
    partitioner.class: "io.confluent.connect.storage.partitioner.HourlyPartitioner"
    locale: "en-US"

Here's my producer:

package kafka;

import com.github.javafaker.Faker;
import java.util.Random;
import org.apache.kafka.clients.producer.KafkaProducer;
import org.apache.kafka.clients.producer.ProducerRecord;
import org.apache.kafka.common.serialization.StringSerializer;
import io.confluent.kafka.serializers.protobuf.KafkaProtobufSerializer;
import com.example.CardData;
import java.util.Properties;

public class SendKafkaProto {
  public static void main(String[] args) {
    // Setup Producer Properties
    String bootstrapServers = "127.0.0.1:9092";
    var properties = new Properties();
    properties.setProperty("bootstrap.servers", bootstrapServers);
    properties.setProperty("schema.registry.url", "http://localhost:8081");
    properties.setProperty("key.serializer", StringSerializer.class.getName());
    properties.setProperty("value.serializer", KafkaProtobufSerializer.class.getName());

    KafkaProducer<String, CardData.CreditCard> producer = new KafkaProducer<>(properties);
    // Specify Topic Name
    var topic = "protos_topic_cards";

    // Loop to Produce Fake Data
    for (int i = 0; i < 15; i++) {
      // creating Random object
      Random rd = new Random();
      Faker faker = new Faker();
      String name = faker.name().fullName();
      String countryCode = faker.address().countryCode();
      String cardNumber = faker.business().creditCardNumber();
      Integer typeValue = rd.nextInt(3);
      String currencyCode = faker.country().currencyCode();

      // Serializing to Protobuf based on CreditCard.proto Schema
      var cardData = CardData.CreditCard.newBuilder()
          .setName(name)
          .setCountry(countryCode)
          .setCurrency(currencyCode)
          .setTypeValue(typeValue)
          .setBlocked(false)
          .setCardNumber(cardNumber)
          .build();

      var record = new ProducerRecord<String, CardData.CreditCard>(topic, "Credit Card", cardData);
      // Send to Producer
      producer.send(record);
    }
    producer.flush();
    producer.close();
    // Log success message
    System.out.println("Sent Data Successfully");
  }
}

What could amiss here? Do I need to add the Protobuf converter to wherever my kafka image is mounted? Do I need to use a string converter for the key serializer? There aren't many solutions here online. Thanks!