ValueError: Cannot assign "'1'": "Post.user" must be a "User" instance - django

Question

I am doing a group project for a bootcamp and we just started Django for the back-end. We also are using React for front-end. Our project is basically a knockoff reddit.
We have a User model:
`from django.db import models
class User(models.Model):
firstname = models.CharField(max_length=100)
lastname = models.CharField(max_length=100)
email = models.CharField(max_length=100, unique=True)
username = models.CharField(max_length=32, unique=True)
password = models.CharField(max_length=255)
def __str__(self):
return '%s' % (self.username)`
and a Post model:
`from django.db import models
from auth_api.models import User
class Post(models.Model):
user = models.ForeignKey(User, on_delete=models.CASCADE, null=True)
title = models.CharField(max_length=255)
formBody = models.TextField(null=True, blank=True)
imageURL = models.CharField(max_length=200, null=True, blank=True)
created = models.DateTimeField(auto_now_add=True)`
Our Post Serializers(pretty unfamiliar with this):
`from rest_framework import serializers
from .models import Post
class PostSerializer(serializers.ModelSerializer):
user = serializers.CharField(required=True)
class Meta:
model = Post
fields = ('id', 'user', 'title', 'formBody', 'imageURL', 'created',)`
And our Post Views:
`from django.shortcuts import render
from rest_framework import generics
from .serializers import PostSerializer
from .models import Post
from auth_api.models import User
class PostList(generics.ListCreateAPIView):
queryset = Post.objects.all().order_by('id')
serializer_class = PostSerializer
class PostDetail(generics.RetrieveUpdateDestroyAPIView):
queryset = Post.objects.all().order_by('id')
serializer_class = PostSerializer`
The idea was when a user created a post their info would be saved with the post so that way when we display the post we could say who created at. Also we could have a user profile that could see all of their posts. I assumed that what would happen is the user info would get saved inside a object in the user column, but the first way we tried only saved the userID and we couldn't access any of the users info. The second way(what we have now) keeps giving us this error: ValueError: Cannot assign "'1'": "Post.user" must be a "User" instance.The 1 is the userID that we pass in from the frontend of the user that created the post. I am unsure of where to go from here and have been stuck for a while on this. Hopefully I provided enough info