Spring Kafka outboundChannelAdapter's control does not return back in the integration flow - spring-integration

Question

After a messsage is sent, it gets published to Kafka topic but the Message from KafkaSuccessTransformer does not return back to the REST controller. I am trying to return the message as-is if sent successfully but nothing after Kafka handler seems to be invoked.
#MessagingGateway
public interface MyGateway<String, Message<?>> {
#Gateway(requestChannel = "enrollChannel")
Message<?> sendMsg(#Payload String payload);
}
------------------------
#RestController
public class Controller {
MyGateway<String, Message<?>> myGateway;
#PostMapping
public Message<?> send(#RequestBody String request) throws Exception {
Message<?> resp = myGateway.sendMsg(request);
log.info("I am back"); // control doesn't come to this point
return resp;
}
}
--------------------------
#Component
public class MyIntegrationFlow {
KafkaSuccessTransformer stransformer;
#Bean
public MessageChannel enrollChannel() {
return new DirectChannel();
}
#Bean
public MessageChannel kafkaSuccessChannel() {
return new DirectChannel();
}
#Bean
public IntegrationFlow enrollIntegrationFlow() {
return IntegrationFlows.from("enrollChannel")
//another transformer which turns the string to Message<?>
.handle(Kafka.outboundChannelAdapter(kafkaTemplate) //kafkaTemplate has the necesssary config
.topic("topic1")
.messageKey(messageKeyFunction -> messageKeyFunction.getHeaders()
.get("key1")
.sendSuccessChannel("kafkaSuccessChannel"));
}
#Bean
public IntegrationFlow successfulKafkaSends() {
return f -> IntegrationFlows.from("kafkaSuccessChannel").transform(stransformer);
}
}
--------------
#Component
public class KafkaSuccessTransformer {
#Transformer
public Message<?> transform(Message<?> message) {
log.info("Message is sent to Kafka");
return message; //control comes here but does not return to REST controller
}
}

Answer 1

Channel adapters are for one-way traffic; there is no result.
Add a publishSubscribe channel with two subflows; the second one can be just a bridge to nowhere - .bridge() ends the flow. It will then return the outbound message to the gateway.
See https://docs.spring.io/spring-integration/docs/current/reference/html/dsl.html#java-dsl-subflows
Per Artem:
Something is off in the configuration or code. The logic is like this: processSendResult(message, producerRecord, sendFuture, getSendSuccessChannel());. Then: getMessageBuilderFactory().fromMessage(message). So, the replyChannel header is present in this "success" message. Therefore that transform(stransformer) should really produce its return to the replyChannel for a gateway in the beginning. Only the problem could be in the KafkaSuccessTransformer code where it does not copy request message headers for reply message. Please, share its whole code.