RabbitMQ messages are not recieved in order by the listener - rabbitmq

Question

I have a scenario where the order of messages received at the receiving end is some times not in order.
My scenario:
MACHINE A:
I am sending a series of messages(around 12 messages) from machine A to machine B over rabbitMQ shovel.
The messages are are of different sizes. The over all size of 12 messages is close to 8mb.
Once the 12 messages are sent, i am also sending "complete message" in the end to MACHINE B.
MACHINE B:
This is the recieving machine. This machine has a single listener. It recieves all the messages sent by MACHINE A. Once it recieves "sending complete", its obvious that this is the last message from MACHINE A and MACHINE B starts processing all the messages that were recieved.
MACHINE B Configiration
<rabbit:listener-container
connection-factory="connectionFactory">
<rabbit:listener ref="onMessageCommand"
queue-names="CommandQueue" />
</rabbit:listener-container>
<bean id="onMessageCommand"
class="com.mypackage.command.messaging.OnMessageListner">
<property name="callBackObject" ref="callbackDisEvent" />
<property name="template" ref="amqpTemplate" />
</bean>
<bean id="callbackDisEvent" class="com.mypackage.command.OperationSettingsListener"></bean>
MACHINE A CODE
public void sendMessage(String messageToSend,String machineBID)
{
Message sendMessage = new Message(messageToSend, new MessageProperties());
RabbitTemplate rabbitTemplate =
messagingApplContext.getBean(RabbitTemplate.class);
rabbitTemplate.send(message, machineBID + ".command");
}
ISSUE:
Some times i am observing that one "sending complete" is recived by the MACHINE B just before some setting. Ideally "sending complete" should always be the last message recived by the MACHINE B.
May i please know what can be the issue here.

Answer 1

Make sure you are using message acknowledgements. More info here https://www.rabbitmq.com/confirms.html

Answer 2

Can you please provide some links for sample programs to implement scoped operations in the right manner. or a sample code will also suffice
The link I provided you has this example:
Collection<?> messages = getMessagesToSend();
Boolean result = this.template.invoke(t -> {
messages.forEach(m -> t.convertAndSend(ROUTE, m));
t.waitForConfirmsOrDie(10_000);
return true;
});
You just have to make sure all the sends are performed within the scope of an invoke call...
Boolean result = this.template.invoke(t -> {
...
t.send(...)
...
t.send(...)
...
return true;
}
And they will all go on the same channel. The return doesn't have to be boolean, it can be anything you want, even null.
this.template.invoke(t -> {
...
t.send(...)
...
t.send(...)
...
return null;
}