I got a few problems of GET /js/bootstrap.bundle.min.js HTTP/1.1" 404, the same goes for the bootstrap.min.css file which I referred to in my basic.html. The reason is due to the css and js folders are not stored in the static directory, Flask looks for the css and js from the static folder.
the bootstrap4 files can be downloaded from getbootstrap website.
The CSS and JS folders were previously in their own directories and not copied to the static folders, after they were in the static folders the css and js loaded as normal.
cyruslab 