python3 does not see a pip-installed package, but python does, despite both being python3.9

[nachogoro]

Minimal reproduction steps

1. Create a new project (e.g. mkdir -p ~/projects/test-project)
2. Create its own virtual environment:

$ cd ~/projects/test-project/
$ pyenv install 3.9.0
$ pyenv virtualenv 3.9.0 testproject-venv
$ pyenv local testproject-venv

3. Create a simple script which requires a missing package:
   $ printf "from money import Money\nprint(\"Success\")" > main.py
4. Attempting to execute the script fails as expected:

$ python3 main.py 
Traceback (most recent call last):
  File "/home/ng/projects/test-project/main.py", line 1, in <module>
    from money import Money
ModuleNotFoundError: No module named 'money'

5. Install the missing package:
   $ pip install money
6. Re-attempt to launch the script and see it fail when using python3 but succeeding with python:

$ python main.py 
Success
$ python3 main.py 
Traceback (most recent call last):
  File "/home/ng/projects/test-project/main.py", line 1, in <module>
    from money import Money
ModuleNotFoundError: No module named 'money'

Both python and python3 are aliases to the same binary:

$ ls -lh $(pyenv which python)
lrwxrwxrwx 1 ng ng 9 Dec  6 15:04 /home/ng/.pyenv/versions/testproject-venv/bin/python -> python3.9
$ ls -lh $(pyenv which python3)
lrwxrwxrwx 1 ng ng 9 Dec  6 15:04 /home/ng/.pyenv/versions/testproject-venv/bin/python3 -> python3.9

What am I missing? Thanks in advance :)

[grizmin]

What you miss is that pyenv which python doesn't guarantee you, that you execute python3 from this path.
What is the output of command -V python3 ?