Unable to add pages and sections using jupyter lab

[ssathar]

I installed jupyter-flex using pip install and unable to add pages and rows as described in the documentation.
I am using JupyterLab to create the file. and added cell tags by clicking on the double cog icon. Tried running:

jupyter nbconvert --to flex test-layout.ipynb --execute

The resulting html file shows only a single row, and no pages. Not sure if I'm missing any settings. Appreciate your help!