Went through all of the documentation here: https://docs.microsoft.com/en-us/microsoftteams/platform/build-your-first-app/build-and-run and repeated it for the letter. I could run the application Hello World on https://localhost:3000/Tab, but when I tried to sideload in the Teams, there was a problem.
I followed step by step what we need to do for sideloading the app in Teams and I gave the permission to upload personal application in Teams using my admin account. But when I opened the https://localhost:3000/Tab and click the bouton add for installing this app in Teams, Teams said: there is a problem.
Any help appreciated.