If all users are experiencing access denied even after configuring the access group correctly, your other configurations may require changes.
Check Preference and Device Time
check if the device timezone and the preference timezone are matching.
Check Settings > Preference > Time Zone
Check Device > Select Device > Time Zone
If you're using automatic user sync (default configuration), the user may not be properly transferred to the device even if there is no exclamation mark signaling sync error.
1. First check that the device network connection is stable
2. Choose your device and click Sync Device.
If this doesn't resolve the issue, proceed with below:
1. Select your devices that requires synchronization
2. Click ...
3. Select Delete Data & Sync Device
This will force sync the device. If you have many users this may take a while.
For more details, refer to [BioStar 2] Delete & Sync Device (Force Device Synchronization with Server)