using findOne in mongodb to find by id - node.js

Question

I'm making a tapTracker app with MEVN stack and there is a page with all of songs
and i want that when i click on a single song make app to open this single song only ...
IN THE FRONT END ==>
so i make route from songs.vue '{that songs page}' to viewSong.vue
<v-btn dark class="cyan darken-3" v-on:click="navigateTo({name: 'song',
params: {songId: song._id}})"> View </v-btn>
after that in viewsong.vue i make a show function with id param
<template>
<h1></h1>
</template>
<script>
import songsServices from '#/services/songsServices'
export default {
data () {
return {
song: null
}
},
async mounted () {
const songId = this.$store.state.route.params.songId
this.song = await songsServices.show(songId)
}
}
</script>
then i make an api with it to send that to back-end server in
songServices.js
show (songId) {
return Api().get(`songs/${songId}`)
}
IN THE BACK END 'SERVER' ==>
i make get http req in router.js
app.get('/songs/:songId', songsController.show)
songsController.js
async show(req,res) {
try {
const Song = await Songs.findOne({_id: req.params.songId})
res.send(song)
} catch (error) {
res.status(400).send('error: error when tring to fetch songs!!!')
console.log(error)
}
}
in postman when i make a get req with this param it give me error
where is the problem ??
hint this is the project url on github
https://github.com/mohamedAdel01/tapTracker