Hi I am using the following code to publish messages from flink to Kafka.

final Properties props = new Properties();

        props.put(ProducerConfig.ACKS_CONFIG, "all");
        props.put(ProducerConfig.KEY_SERIALIZER_CLASS_CONFIG, "org.apache.kafka.common.serialization.StringSerializer");
        props.put(ProducerConfig.VALUE_SERIALIZER_CLASS_CONFIG,
                "org.apache.kafka.common.serialization.StringSerializer");
        props.put("security.protocol", "SASL_SSL");
        props.put("sasl.mechanism", "PLAIN");
        props.put("client.dns.lookup", "use_all_dns_ips");
        props.put("group.id", "flink-consumer-1");

DataStream<String> enrichedJson = flattenedJson.map(new MapFunction<JsonNode, String>() {

            public String map(JsonNode value) throws Exception {
                Integer customerId = value.get("customerId").intValue();
                ObjectMapper mapper = new ObjectMapper(); 
                
                String json = mapper.writeValueAsString(map.get(customerId).get("name"));
                JsonNode jsonNode = mapper.readTree(json);
                JsonNode obj = ((ObjectNode) value).set("name", jsonNode );
                
                json = mapper.writeValueAsString(map.get(customerId).get("mobileNumber"));
                jsonNode = mapper.readTree(json);
                obj = ((ObjectNode) value).set("mobileNumber", jsonNode );
                return obj.asText();
            }
            
            
        });

        enrichedJson.print();
        
        FlinkKafkaProducer010 <String> producer = new FlinkKafkaProducer010<String>("ENRICHED_CUSTOMER", new SimpleStringSchema(), props);
        enrichedJson.addSink(producer);

I am getting the below mentioned error for serilization

Exception in thread "main" org.apache.flink.runtime.client.JobExecutionException: org.apache.kafka.common.errors.SerializationException: Can't convert value of class [B to class org.apache.kafka.common.serialization.StringSerializer specified in value.serializer
    at org.apache.flink.runtime.minicluster.MiniCluster.executeJobBlocking(MiniCluster.java:625)
    at org.apache.flink.streaming.api.environment.LocalStreamEnvironment.execute(LocalStreamEnvironment.java:121)
    at flink.KafkaFlink.main(KafkaFlink.java:123)
Caused by: org.apache.kafka.common.errors.SerializationException: Can't convert value of class [B to class org.apache.kafka.common.serialization.StringSerializer specified in value.serializer
    at org.apache.kafka.clients.producer.KafkaProducer.doSend(KafkaProducer.java:955)
    at org.apache.kafka.clients.producer.KafkaProducer.send(KafkaProducer.java:912)
    at org.apache.flink.streaming.connectors.kafka.FlinkKafkaProducer010.invoke(FlinkKafkaProducer010.java:382)
    at org.apache.flink.streaming.api.operators.StreamSink.processElement(StreamSink.java:56)
    at org.apache.flink.streaming.runtime.tasks.OperatorChain$CopyingChainingOutput.pushToOperator(OperatorChain.java:560)
    at org.apache.flink.streaming.runtime.tasks.OperatorChain$CopyingChainingOutput.collect(OperatorChain.java:535)
    at org.apache.flink.streaming.runtime.tasks.OperatorChain$CopyingChainingOutput.collect(OperatorChain.java:515)
    at org.apache.flink.streaming.runtime.tasks.OperatorChain$BroadcastingOutputCollector.collect(OperatorChain.java:630)
    at org.apache.flink.streaming.runtime.tasks.OperatorChain$BroadcastingOutputCollector.collect(OperatorChain.java:583)
    at org.apache.flink.streaming.api.operators.AbstractStreamOperator$CountingOutput.collect(AbstractStreamOperator.java:679)
    at org.apache.flink.streaming.api.operators.AbstractStreamOperator$CountingOutput.collect(AbstractStreamOperator.java:657)
    at org.apache.flink.streaming.api.operators.StreamMap.processElement(StreamMap.java:41)
    at org.apache.flink.streaming.runtime.tasks.OperatorChain$CopyingChainingOutput.pushToOperator(OperatorChain.java:560)
    at org.apache.flink.streaming.runtime.tasks.OperatorChain$CopyingChainingOutput.collect(OperatorChain.java:535)
    at org.apache.flink.streaming.runtime.tasks.OperatorChain$CopyingChainingOutput.collect(OperatorChain.java:515)
    at org.apache.flink.streaming.api.operators.AbstractStreamOperator$CountingOutput.collect(AbstractStreamOperator.java:679)
    at org.apache.flink.streaming.api.operators.AbstractStreamOperator$CountingOutput.collect(AbstractStreamOperator.java:657)
    at org.apache.flink.streaming.api.operators.TimestampedCollector.collect(TimestampedCollector.java:51)
    at flink.KafkaFlink$1.flatMap(KafkaFlink.java:90)
    at flink.KafkaFlink$1.flatMap(KafkaFlink.java:1)
    at org.apache.flink.streaming.api.operators.StreamFlatMap.processElement(StreamFlatMap.java:50)
    at org.apache.flink.streaming.runtime.tasks.OperatorChain$CopyingChainingOutput.pushToOperator(OperatorChain.java:560)
    at org.apache.flink.streaming.runtime.tasks.OperatorChain$CopyingChainingOutput.collect(OperatorChain.java:535)
    at org.apache.flink.streaming.runtime.tasks.OperatorChain$CopyingChainingOutput.collect(OperatorChain.java:515)
    at org.apache.flink.streaming.api.operators.AbstractStreamOperator$CountingOutput.collect(AbstractStreamOperator.java:679)
    at org.apache.flink.streaming.api.operators.AbstractStreamOperator$CountingOutput.collect(AbstractStreamOperator.java:657)
    at org.apache.flink.streaming.api.operators.StreamMap.processElement(StreamMap.java:41)
    at org.apache.flink.streaming.runtime.tasks.OperatorChain$CopyingChainingOutput.pushToOperator(OperatorChain.java:560)
    at org.apache.flink.streaming.runtime.tasks.OperatorChain$CopyingChainingOutput.collect(OperatorChain.java:535)
    at org.apache.flink.streaming.runtime.tasks.OperatorChain$CopyingChainingOutput.collect(OperatorChain.java:515)
    at org.apache.flink.streaming.api.operators.AbstractStreamOperator$CountingOutput.collect(AbstractStreamOperator.java:679)
    at org.apache.flink.streaming.api.operators.AbstractStreamOperator$CountingOutput.collect(AbstractStreamOperator.java:657)
    at org.apache.flink.streaming.api.operators.StreamSourceContexts$NonTimestampContext.collect(StreamSourceContexts.java:104)
    at org.apache.flink.streaming.api.operators.StreamSourceContexts$NonTimestampContext.collectWithTimestamp(StreamSourceContexts.java:111)
    at org.apache.flink.streaming.connectors.kafka.internals.AbstractFetcher.emitRecordWithTimestamp(AbstractFetcher.java:398)
    at org.apache.flink.streaming.connectors.kafka.internal.Kafka010Fetcher.emitRecord(Kafka010Fetcher.java:89)
    at org.apache.flink.streaming.connectors.kafka.internal.Kafka09Fetcher.runFetchLoop(Kafka09Fetcher.java:154)
    at org.apache.flink.streaming.connectors.kafka.FlinkKafkaConsumerBase.run(FlinkKafkaConsumerBase.java:738)
    at org.apache.flink.streaming.api.operators.StreamSource.run(StreamSource.java:87)
    at org.apache.flink.streaming.api.operators.StreamSource.run(StreamSource.java:56)
    at org.apache.flink.streaming.runtime.tasks.SourceStreamTask.run(SourceStreamTask.java:99)
    at org.apache.flink.streaming.runtime.tasks.StreamTask.invoke(StreamTask.java:306)
    at org.apache.flink.runtime.taskmanager.Task.run(Task.java:703)
    at java.base/java.lang.Thread.run(Thread.java:834)
Caused by: java.lang.ClassCastException: class [B cannot be cast to class java.lang.String ([B and java.lang.String are in module java.base of loader 'bootstrap')
    at org.apache.kafka.common.serialization.StringSerializer.serialize(StringSerializer.java:29)
    at org.apache.kafka.common.serialization.Serializer.serialize(Serializer.java:62)
    at org.apache.kafka.clients.producer.KafkaProducer.doSend(KafkaProducer.java:952)
    ... 43 more