I finally managed to solve my problem. I created a repo from scratch on github (my repo is now at: GitHub - badgiojuni/Bear-finder: I successfully deployed a web application from Lesson2/3 of fastai book on mybinder & heroku. It allows to differentiate a bear from a teddy bear, you can find the app at: https://bear-app69.herokuapp.com/) and used the ‘requirements.txt’ from How to Deploy Fast.ai Models? (Voilà , Binder and Heroku) | by Aravinda Gayan | unpackAI | Medium and the steps from Deploying your notebook as an app under 10 minutes to deploy it on Binder. It worked well, I think I did smth wrong when I followed the git related steps (the git track “*.pkl” command wasn’t of any use for me, instead I just added the export.pkl file to the cloned repo and it worked well).
It worked as well on heroku by adding a procfile file as it is explained in the medium article from above. This was the only thing I needed to add to make it work on heroku after having made it work on binder. Thanks for the helpful indications on the forum