If you are using either the Better Balance or Sugar Smart plan this is because activity bites are set to "Do Not Use" by default as it is encouraged to not eat your activity bites. If you would like to instead use your activity bites, you can change your settings:
- Go the Settings gear
- Preferences > Tap Settings
- Tap Activity Allowance
- Set it to use your activity allowance either Daily or Weekly depending on which you prefer