Mongo kafka sink connector: How to convert messages which are protobuf encoded in aws msk?

I’m integrating AWS msk connector with mongodb using MongoDB Connector. I see here that we can give the value converter configurations as value.converter=io.confluent.connect.protobuf.ProtobufConverter. But when creating the sink connector in aws console it gives me Invalid configuration error. I did able to peek at source code from source code but didnt see any protobuf implementation of converters.