I've connected my HRM to 24GO but the workout I'm doing isn't displaying my calories burned?

The reason this is happening is you do not have weight and height set in your user profile.  These two measurements are needed in order for 24GO to calculate an estimation of calories burned.  Those that skipped the registration questions when they first logged into 24GO will need to manually enter their measurements.

Directions to add these measurements in your profile:
1) Open the 24GO application.
2) Tap on the "Dashboard" icon (figure inside circle - top right of screen).
3) Tap on blue gear icon (next to your picture or larger figure inside circle).
4) Tap on "About Me".
5) Enter your "Height" and "Weight" and tap on "Save Changes".

Now if you're wearing a HRM and it's connected to 24GO when you do a workout you'll see calories being burned.