ValueError: Cannot assign "1": "Topic.board" must be a "Board" instance

I know there are a bunch of questions addressing this issue, but I haven't solved it out yet. please any help i tried many solutions but didn't work

models.py

class Board(models.Model):
    name = models.CharField(max_length=50,unique=True)
    description = models.CharField(max_length=150)

    def __str__(self):     
        return self.name

class Topic(models.Model):
    subject = models.CharField(max_length=255)
    board = models.ForeignKey(Board,related_name='topics',on_delete=models.CASCADE)
    created_by = models.ForeignKey(User,related_name='topics',on_delete=models.CASCADE)
    created_dt = models.DateTimeField(auto_now_add=True)

class Post(models.Model):
    message = models.TextField(max_length=4000)
    topic = models.ForeignKey(Topic, related_name='posts',on_delete=models.CASCADE)
    created_by = models.ForeignKey(User,related_name='posts',on_delete=models.CASCADE)
    created_dt = models.DateTimeField(auto_now_add=True)

view.py

def new_topic(request,board_id):
    board = get_object_or_404(Board,pk=board_id)
    if request.method == 'POST':
        subject = request.POST['subject']
        message = request.POST['message']
        user = User.objects.first()
    
        topic = Topic.objects.create(
            subject=subject,
            board=board_id,
            created_by=user
        )

        post = Post.objects.create(
            message=message,
            topic=topic,
            created_by=user
    )

new_topic.html

{% extends 'base.html' %}

{% block title %}Start a New Topic{% endblock %}

{% block breadcrumb %}
  <li class="breadcrumb-item"><a href="{% url 'home' %}">Boards</a></li>
  <li class="breadcrumb-item"><a href="{% url 'board_topics' board.pk %}">{{ board.name }}</a></li>
  <li class="breadcrumb-item active">New topic</li>
{% endblock %}

{% block content %}
  <form method="post">
    {% csrf_token %}
    <div class="form-group">
      <label for="id_subject">Subject</label>
      <input type="text" class="form-control" id="id_subject" name="subject">
    </div>
    <div class="form-group">
      <label for="id_message">Message</label>
      <textarea class="form-control" id="id_message" name="message" rows="5"></textarea>
    </div>
    <button type="submit" class="btn btn-success">Add</button>
  </form>
{% endblock %} 

I'm fairly new to Django. How would I go about resolving that?