Apps model of not able to create from admin site. | DatabaseError at /admin/transport/branch/add/ No exception message supplied

Hi,
I have created app named as transport.
There is diffrent models.
I register it in admin also.
When I am trying to create objects from admin site I am not able to create it.
Error

DatabaseError at /admin/transport/branch/add/
No exception message supplied
Request Method:	POST
Request URL:	http://127.0.0.1:8000/admin/transport/branch/add/
Django Version:	4.1
Exception Type:	DatabaseError
Exception Location:	C:\Python310\lib\site-packages\djongo\cursor.py, line 81, in fetchone
Raised during:	django.contrib.admin.options.add_view
Python Executable:	C:\Python310\python.exe
Python Version:	3.10.2
Python Path:	
['W:\\MySoftware\\logistics',
 'C:\\Python310\\python310.zip',
 'C:\\Python310\\DLLs',
 'C:\\Python310\\lib',
 'C:\\Python310',
 'C:\\Python310\\lib\\site-packages',
 'C:\\Python310\\lib\\site-packages\\win32',
 'C:\\Python310\\lib\\site-packages\\win32\\lib',
 'C:\\Python310\\lib\\site-packages\\Pythonwin']
Server time:	Sun, 21 Aug 2022 14:18:12 +0000
**app's models.py**

class Branch(models.Model):
id = models.AutoField(primary_key=True)
name = models.CharField(max_length = 100)
cityId = models.ForeignKey(City, on_delete=models.CASCADE)
isActive = models.BooleanField(default=1)
createdTime = models.DateTimeField(editable=False, default=datetime.now)
updatedTime = models.DateTimeField(editable=False, default=datetime.now)
def str(self) → str:
if self.isActive:
return str(self.id)+" “+self.name+” “+str(self.cityId)+” 1"
else:
return str(self.id)+" “+self.name+” “+str(self.cityId)+” 0"

**app's admin.py**

from django.contrib import admin

Register your models here

from .models import *

admin.site.register([Party,Branch,BookingRegister])

**app's views.py**
![image|690x416](upload://4YdvEd90nq8et8xjkAiFG6oTwKz.png)


When I am creating Branch object from admin site I am not able to create it.
it show error DatabaseError at /admin/transport/branch/add/
No exception message supplied.
Can anyone please help in this.
Thanks