Cortextools not able to get metric names from a Grafana dashboard

I am trying to execute cortextools
to get metric names used in a dashboard file but it is not giving any output. Can someone let me know what is going wrong?

debrajmanna@Debrajs-MacBook-Air ~ % cortextool  --log.level=debug analyse dashboard ./tempo-reads-dashboard.json

INFO[0000] log level set to debug

Version

debrajmanna@Debrajs-MacBook-Air ~ % cortextool version
version 0.11.3
checking latest version... You are on the latest version

The dashboard JSON file is placed here as I am not able to attach a file to this post as I am a new user.

Could someone please let me know what is going wrong, or are there any alternative tools I can use to retrieve the metric names used in the Grafana dashboard file?