Django: signal doesn't work well with ForeignKey

Question

models.py

from django.db import models

class Post(models.Model):
    text = models.TextField()
    approved = models.BooleanField(default=False)
    group = models.ForeignKey('bot_users.BotUserGroup', on_delete=models.SET_NULL, null=True, blank=True)


from django.conf import settings
from django.db import models
import os

class PostMedia(models.Model):
    post = models.ForeignKey(Post, on_delete=models.CASCADE, related_name='mediafiles')
    media = models.FileField(upload_to='post_media/', blank=True)
    absolute_media_path = models.CharField(max_length=255, blank=True)

    def save(self, *args, **kwargs):
        self.absolute_media_path = self.get_absolute_media_path()
        return super().save(*args, **kwargs)

    def get_absolute_media_path(self):
        return os.path.join(settings.BASE_DIR, self.media.path)


#Post.objects.last().mediafiles.last().absolute_media_path

services.py (functions for aiogram bot and django)

async def get_post_path(post_id):
    url = f'http://localhost:8000/api/get_media_urls/{post_id}/'
    async with aiohttp.ClientSession() as session:
        async with session.get(url) as response:
            if response.status == 200:
                data_list = await response.json()
                return data_list
            else:
                return None


async def register_manager(CHAT_ID: str):
    fake = Faker()

    username = fake.user_name()
    password = fake.password()

    await bot.send_message(CHAT_ID, f'username: {username}\npassword: {password}\nadmin-panel: http://localhost:8000/admin', reply_markup=set_manager_kb())



# async def send_post(instance):
#     admin_id = '679553167'

#     await bot.send_message(admin_id, f'{instance}', reply_markup=set_post_kb())



async def send_post(post):

    message = post.split('\n')


    user_id = '679553167'

    post_id = message[0]



    media = []


    media_paths = await get_post_path(post_id)


    if media_paths:
        for photo_path in media_paths:
            if photo_path.lower().endswith(('.jpg', '.jpeg', '.png')):
                media_type = types.InputMediaPhoto
            elif photo_path.lower().endswith(('.mp4', '.avi', '.mkv')):
                media_type = types.InputMediaVideo
            else:
                continue
            photo_file = open(photo_path, 'rb')
            input_media = media_type(media=types.InputFile(photo_file))
            media.append(input_media)


        media[0]["caption"] = message[1]

        await bot.send_media_group(chat_id=user_id, media=media, reply_markup=set_post_kb())
        photo_file.close()
    else:
        await bot.send_message(user_id, message[1], reply_markup=set_post_kb())

signals.py

from django.db.models.signals import post_save
from django.dispatch import receiver
from .models import Post, PostMedia
from bot.django_services import send_post, get_post_path
from asgiref.sync import async_to_sync

@receiver(post_save, sender=PostMedia)
def post_created(sender, instance, created, **kwargs):
    if created:
        send_post_sync = async_to_sync(send_post)
        if instance.post.group:
            print(instance.absolute_media_path)
            send_post_sync(f'{instance.post.id}\n{instance.post.text}\n{instance.post.group.id}')
        else:
            print(instance.absolute_media_path)
            send_post_sync(f'{instance.post.id}\n{instance.post.text}')

The thing is I get an empty list of media_paths = await get_post_path(post_id), although Post have a few PostMedia instances with FK.
Also, as you can see, I have prints in my signals and that's what they show:

[13/Aug/2023 00:37:48] "GET /admin/posts/post/add/ HTTP/1.1" 200 18144
[13/Aug/2023 00:37:49] "GET /admin/jsi18n/ HTTP/1.1" 200 3343
C:\Users\hp\Desktop\job\media\depositphotos_59977559-stock-photo-hands-holding-word-about-us.jpg
[13/Aug/2023 00:38:01] "GET /api/get_media_urls/51/ HTTP/1.1" 200 2
C:\Users\hp\Desktop\job\media\Green_card_2_X2Wbqbu.jpg
[13/Aug/2023 00:38:04] "GET /api/get_media_urls/51/ HTTP/1.1" 200 2
[13/Aug/2023 00:38:04] "POST /admin/posts/post/add/ HTTP/1.1" 302 0
[13/Aug/2023 00:38:04] "GET /admin/posts/post/ HTTP/1.1" 200 16314
[13/Aug/2023 00:38:04] "GET /admin/jsi18n/ HTTP/1.1" 200 3343

So, they print what I nedd, but not in one list (firstly C:\Users\hp\Desktop\job\media\depositphotos_59977559-stock-photo-hands-holding-word-about-us.jpg, then C:\Users\hp\Desktop\job\media\Green_card_2_X2Wbqbu.jpg etc.)

I've tried make a sender=Post, but it didn't work at all.