Why is there an error when migrating to Django?

Question

Django

Created a model

from django.db import models
from django.contrib.postgres.fields import ArrayField

class VKGROUPREQUESTS(models.Model):
    id_group = models.CharField(max_length=100)
    count_posts = models.IntegerField(default=0)
    date_time_request = models.DateField(auto_now_add=True)
    file_path = models.CharField(max_length=256, blank=True)
    data = ArrayField(models.CharField(max_length=200), blank=True)

    def __str_(self):
        return self.id_group

    class Meta:
        ordering = ['id_group']
        verbose_name = 'Запрос'
        verbose_name_plural = 'Запросы'



class VKGROUP(models.Model):
    id_group = models.ForeignKey(VKGROUPREQUESTS, on_delete=models.CASCADE)

    @property
    def __str__(self):
        return self.id_group
    class Meta:
        ordering = ['id_group']
        verbose_name = 'Группа ВК'
        verbose_name_plural = 'Группы ВК'

The makemigrations command goes well, but the migration command throws an error:
File "C:\Program Files\Anaconda\lib\json\encoder.py", line 180, in default
o.__class__.__name__)
TypeError: Object of type ' datetime' is not JSON serializable
DB - Postgres