Vue <script setup> reactivity not working

Im trying the <script setup> syntax in vue and wondering why reactivity is not working. What’s wrong here?

<template>
    <button @click="changeButtonText">{{ buttonText }}</button>
</template>

<script setup>
import { ref } from 'vue'

let buttonText = ref("Foo")

function changeButtonText() {
    buttonText = "Bar"
}
</script>

Tried without ref().
Tried with buttonText = ref("Bar"). No effect

>Solution :

In your function you have to change
buttonText = "Bar" to buttonText.value="Bar"

For more info on reactivity see: https://vuejs.org/api/reactivity-core.html#ref