Why does this not work?

slices1.go

package main

import "fmt"

type myStruct struct {
  id       int
  messages []Message
}

type Message struct {
  MessageText  string
}

func (s myStruct) addMessage(m Message) {
  s.messages = append(s.messages, m)
}

func main() {
	s1 := myStruct{
	  id: 1,
	  messages: make([]Message, 0),
	}

	m1 := Message{MessageText: "Hey"}

	s1.addMessage(m1)
	s1.addMessage(m1)
	s1.addMessage(m1)

	fmt.Println(s1.messages) // immer leer
}

The error lies in the difference between a pointer receiver and a value receiver