Deleted a folder, get ModuleNotFoundError: No module named "api" - django

Question

I am using Django and trying to use Django Rest Framework as well.
Since I had never used Django Rest Framework, I did a kind of tutorial by following an article. To do this, I created a new app by entering python manage.py startapp app.
After I finished the tutorial, I deleted this app in order to work on my project.
However, when I try to make the server run I got this error.
(venv) (base) MacBook-Air-4:extra_exchange user$ python manage.py makemigrations
Traceback (most recent call last):
File "manage.py", line 22, in <module>
main()
File "manage.py", line 18, in main
execute_from_command_line(sys.argv)
File "/Users/user/Desktop/my_project/extra_exchange/venv/lib/python3.7/site-packages/django/core/management/__init__.py", line 401, in execute_from_command_line
utility.execute()
File "/Users/user/Desktop/my_project/extra_exchange/venv/lib/python3.7/site-packages/django/core/management/__init__.py", line 395, in execute
self.fetch_command(subcommand).run_from_argv(self.argv)
File "/Users/user/Desktop/my_project/extra_exchange/venv/lib/python3.7/site-packages/django/core/management/base.py", line 330, in run_from_argv
self.execute(*args, **cmd_options)
File "/Users/user/Desktop/my_project/extra_exchange/venv/lib/python3.7/site-packages/django/core/management/base.py", line 368, in execute
self.check()
File "/Users/user/Desktop/my_project/extra_exchange/venv/lib/python3.7/site-packages/django/core/management/base.py", line 396, in check
databases=databases,
File "/Users/user/Desktop/my_project/extra_exchange/venv/lib/python3.7/site-packages/django/core/checks/registry.py", line 70, in run_checks
new_errors = check(app_configs=app_configs, databases=databases)
File "/Users/user/Desktop/my_project/extra_exchange/venv/lib/python3.7/site-packages/django/core/checks/urls.py", line 13, in check_url_config
return check_resolver(resolver)
File "/Users/user/Desktop/my_project/extra_exchange/venv/lib/python3.7/site-packages/django/core/checks/urls.py", line 23, in check_resolver
return check_method()
File "/Users/user/Desktop/my_project/extra_exchange/venv/lib/python3.7/site-packages/django/urls/resolvers.py", line 408, in check
for pattern in self.url_patterns:
File "/Users/user/Desktop/my_project/extra_exchange/venv/lib/python3.7/site-packages/django/utils/functional.py", line 48, in __get__
res = instance.__dict__[self.name] = self.func(instance)
File "/Users/user/Desktop/my_project/extra_exchange/venv/lib/python3.7/site-packages/django/urls/resolvers.py", line 589, in url_patterns
patterns = getattr(self.urlconf_module, "urlpatterns", self.urlconf_module)
File "/Users/user/Desktop/my_project/extra_exchange/venv/lib/python3.7/site-packages/django/utils/functional.py", line 48, in __get__
res = instance.__dict__[self.name] = self.func(instance)
File "/Users/user/Desktop/my_project/extra_exchange/venv/lib/python3.7/site-packages/django/urls/resolvers.py", line 582, in urlconf_module
return import_module(self.urlconf_name)
File "/Users/user/opt/anaconda3/lib/python3.7/importlib/__init__.py", line 127, in import_module
return _bootstrap._gcd_import(name[level:], package, level)
File "<frozen importlib._bootstrap>", line 1006, in _gcd_import
File "<frozen importlib._bootstrap>", line 983, in _find_and_load
File "<frozen importlib._bootstrap>", line 967, in _find_and_load_unlocked
File "<frozen importlib._bootstrap>", line 677, in _load_unlocked
File "<frozen importlib._bootstrap_external>", line 728, in exec_module
File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
File "/Users/user/Desktop/my_project/extra_exchange/extra_exchange/urls.py", line 21, in <module>
path("api/", include("api.urls"))
File "/Users/user/Desktop/my_project/extra_exchange/venv/lib/python3.7/site-packages/django/urls/conf.py", line 34, in include
urlconf_module = import_module(urlconf_module)
File "/Users/user/opt/anaconda3/lib/python3.7/importlib/__init__.py", line 127, in import_module
return _bootstrap._gcd_import(name[level:], package, level)
File "<frozen importlib._bootstrap>", line 1006, in _gcd_import
File "<frozen importlib._bootstrap>", line 983, in _find_and_load
File "<frozen importlib._bootstrap>", line 953, in _find_and_load_unlocked
File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
File "<frozen importlib._bootstrap>", line 1006, in _gcd_import
File "<frozen importlib._bootstrap>", line 983, in _find_and_load
File "<frozen importlib._bootstrap>", line 965, in _find_and_load_unlocked
ModuleNotFoundError: No module named 'api'
On the very last line, it says No module named 'api'.
But as I said, I have already deleted this. I looked for solutions but all solutions tell about already installed files, not deleted files.
I would like you to teach me how to figure it out.
Before I deleted this api file, the structure of files is like this.
project
|
|- app
| |
| |- migrations
| | ...
| |- and everything
|
|- api(deleted folder)
| |
| |- migrations
| | ...
| |- and everything
|
|-my_project
| |
| |- setting.py
| | ...
| |- and everything
|
|-venv
|-manage.py

Answer 1

Actually, I forgot to remove some urls from urls.py, that's why I got the error.
Thank you for watching it. I figured it out.

Answer 2

I just spent almost an hour trying to figure out something similar myself.
I deleted all references to my app from my project but kept getting this error.
I searched the entire project in my IDE (VS Code) for references to the app, but didn't find any. (even reinstalled Django but no luck).
Finally I decided to do a grep within the project folder. Sure enough I found a reference. What happened was that I edited the file, but didn't save it.
Hopefully someone will benefit from my experience.