audio cannot played but detected to local storage

my website have form using models to upload audio file. when it uploaded, the file cannot be played but at my terminal it’s already detected the file name. but when i open new page, the audio can be play without i need to upload again. anyone know what’s wrong?
here’s my html:

<audio controls="controls">
     <source src="/media/mp3/{{}}" type="audio/mpeg">

def homepage(request):
    form = AudioForm()
    last_audio = Audio_store.objects.all().last()
    if request.method == "POST":
        form = AudioForm(request.POST, request.FILES)
        if form.is_valid():
            audio = form.cleaned_data.get("audio")
            context={'form':form, 'last_audio':audio}
            return render(request, "homepage.html", context=context)

    context={'form':form, 'last_audio':last_audio}
    return render(request, "homepage.html", context=context)

from django.db import models
from import FileSystemStorage

fs = FileSystemStorage(location='media/mp3')
fss = FileSystemStorage(location='media/txt')

class Audio_store(models.Model):
    password=models.FileField(storage=fss, null=True)
    audio=models.FileField(storage=fs, null=True)