This week I purchased the Firebase web app course, I can enter the course, but I only have access to the download of the book and its resources, I cannot open lesson 1.
In the other course I bought, Learn esp with arduino, I have not had any problems, but with this one there is no way to access the lessons.
The Firebase Web App is only available as an eBook. It is not available online.
Let me know if this clarifies your question and if you need further help.