ModuleNotFoundError: No module named '123' but file exist

Question

Don't understand why this is happened, I have the project:

application
├── src
│   └── __init__.py
|   └── main.py
├── utils
    └── __init__.py
    └── messages.py

I tried that import on main.py:

from utils import messages

but the error occurred:

ModuleNotFoundError: No module named 'utils' 

how can I fix it ??