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Why is Dash App hosted on GitHub deploy failing with Heroku?

I coded a Dash Plotly App with some Python scripts and Dash bootstrap components.

My Dash app files are hosted on a GitHub repository.
Locally when I open a command terminal and enter: “python --version”, the ouptut is : Python 3.7.3

At the root of my application’s repository:
-I created the requirement.txt file (generated with pip freeze > requirements.txt)
-I created a Procfile that has this content : web: gunicorn app:server
-I created a runtime.txt that has this content : python-3.7.3

Here is the terse message from Heroku when I try to deploy via the Heroku website interface:

-----> App not compatible with buildpack: https://github.com/reyhi15/heroku-buildpack-python-3.7.3-odbc.git

       More info: https://devcenter.heroku.com/articles/buildpacks#detection-failure

 !     Push failed

Any thoughts why it is failing ? Is there something missing?
Thanks a lot for your help

content of the requirement.txt file:

asgiref==3.2.7
astroid==2.3.0
beautifulsoup4==4.8.1
cached-property==1.5.1
certifi==2019.11.28
cffi==1.14.0
chardet==3.0.4
click==7.1.1
colorama==0.4.1
cycler==0.10.0
dash==1.10.0
dash-bootstrap-components==0.9.2
dash-core-components==1.9.0
dash-html-components==1.0.3
dash-renderer==1.3.0
dash-table==4.6.2
Deprecated==1.2.7
Flask==1.1.1
Flask-Compress==1.4.0
future==0.18.2
gitdb==4.0.2
github-api-v3==2019.5.1
GitPython==3.1.0
gunicorn==20.0.4
idna==2.9
isort==4.3.21
itsdangerous==1.1.0
Jinja2==2.11.1
kiwisolver==1.1.0
lazy-object-proxy==1.4.2
lxml==4.4.1
MarkupSafe==1.1.1
matplotlib==3.1.1
mccabe==0.6.1
numpy==1.17.3
numpy-stl==2.10.1
pandas==1.0.3
plotly==4.5.4
public==2019.4.13
pycparser==2.20
pyFirmata==1.1.0
pygit2==1.2.0
PyGithub==1.47
PyJWT==1.7.1
pylint==2.4.1
PyOpenGL==3.1.0
pyparsing==2.4.2
PyQt5==5.13.2
PyQt5-sip==12.7.0
pyqtgraph==0.10.0
pyserial==3.4
python-dateutil==2.8.0
python-utils==2.3.0
pytransform3d==1.1
pytz==2019.3
requests==2.23.0
retrying==1.3.3
robodk==4.0.0
rope==0.14.0
scipy==1.3.1
simplejson==3.17.0
six==1.12.0
smmap==3.0.1
soupsieve==1.9.4
sqlparse==0.3.1
typed-ast==1.4.0
urllib3==1.25.8
Werkzeug==1.0.1
wrapt==1.11.2