My hope in writing this out is that you go "well duh! Of course" and then pretend like you knew this all already. Whether or not you did is up to you.

With communication there is going to be a Sender and a Receiver. These can and will regularly swap around in a healthy relationship. There will also be a Message. The message goes from the sender to the receiver. Often the sender feels most heard when we get confirmation or affirmation that the message was received and it was the same message that we sent. This can happen by repetition (See also Handshaking (computer science)).

It's not all that complicated.

A short time later. A confirmation of the first message or a new message being sent.

There are many ways that a message can go wrong.

Here is a few of them:

Over emphasis - you get the message across but it’s super harsh. "Don't walk on my left side" is heard as "never ever do that ever again"
Under emphasis - you get the message across but it’s a mild form and not taken seriously. "can you make sure you message me when you are running late" becomes "if you remember to text me, that would be great"
Opposite message - you successfully send the opposite message. "I appreciate your attention" becomes "leave me alone"
Wrong message - you successfully sent a different message. "I want you to tell me that you like what I am wearing" becomes "I want you to lie to me to make me feel better"
Under specific - you sent a message but it’s not clear what the specific problem is. Or why you are sending this message. "you need to be a cleaner person" when you wanted to say, "clean your bathroom because there is mould on the walls and it's making you sick"
Over specific - you get the message across but it seems like it only applies to the past and not other similar situations. See also rules-lawyering your relationships - “you said you didn’t want me to go to dinner, you didn’t say anything about lunch”. “you said you didn’t like me holding hands, you didn’t say anything about walking arm in arm... why are you so upset! Come back and talk to me!”
garbled - it’s clear you are sending a message but it’s not clear what. "Hey when you do that thing I wish you would do something different instead". "lets meet up some time to talk".
Incomplete message - "hey can you just..."
Rambling long - Grice's Maxim of quantity (Make your contribution as informative as is required. Do not make your contribution more informative than is required.) - "I was just talking to sally and she said that I should tell you what I was telling her so I decided I would tell you and then I caught the bus here and then I was hungry so I went to get a sandwich and then I decided I would come talk to you..."
Sending a message by accident - you seem to be giving off a message. See “resting bitch face”. "when you cross your arms I think you are angry" "but I was just cold". Also it’s counterpart-

Seeing a message that isn’t there - “you didn’t reply to my text for seventeen minutes so you must hate me and want to break up”. You said "goodbye and not sweet dreams so something must be wrong".

Problems with messages can be to do with one of these errors, or to do with a failure to successfully send and receive a message. For example an interruption while sending can cause a message to be incomplete. If the receiver is not paying attention this can get in the way of a message being sent.

It can also be helpful to be clear what you want someone to do with the message.

Some ideas:

I want you to repeat the message back to me.
I want you to confirm if you agree or disagree.
I want you to do the action I told you to do.
I want you to offer something as an exchange.
I want to know how this message makes you feel.
I want you to have heard the message and not responded.
I want validation from you.
I want support from you.
I want your ideas around solving this problem

See also emotional bids, validation/affirmation from NVC (video), Circling. 4 types of conversation from number 2 - difficult conversations in my list of models of relationships, Filter on the way in, Filter on the way out, A model of arguments. What is a problem?

Meta: I've never seen it written out. My hope is that this simple model can help you think about communication and message sending. It's very simple and doesn't cover barriers to sending a message and many other things but it's a start.