Using {{content}} in the template shows 'selected undefined'

[tmsbn]

I have a template that looks like this

{{content}}

Generate questions based on the above content to quiz me on the topics in this page. Stick to the contents of this page. 

Questions to study this topic:
{{output}}

When I open a note and run this template using Generate & Insert command, I always get an error (as a notice in Obsidian) saying 'selected undefined' although the generation seems to work correctly. Can you take a look?