Can't set a custom heart rate zone in the Fitbit app

[eStrud]

I've found the section under setting that allows me to switch from default to custom heart rate zone. But every time I enter a min and max and sync nothing happens. I want to set my cardio to a different (lower) starting point. It's important it matches the lower threshold from my physio. Is this possible? And why does the custom setting in the dashboard not do anything?

In min and max presumably I am supposed to be entering the lower and upper limits of my custom zone. But nothing happens. Is this a bug?

Cheers

Moderator edit: subject for clarity 

[LiliyaFitbit]

It’s good to see you in the community, @eStrud.

Thanks for the details shared in your post. I understand how you are feeling and appreciate your efforts. I recommend confirming the steps to create your custom heart rate zones:

1. In the Fitbit app, tap the Today tab and tap your profile picture.
2. Tap Heart Rate Zones.
3. Enter your custom zone. For more information, see What are heart-rate zones?

If you continue experiencing difficulties, please try using the fitbit.com dashboard: click the gear icon in the top right > click Settings > Personal Info and enter your custom zone. Sync your device in the Fitbit app. 

Hope this helps.