Since ANT+ doesn’t work, I got a Bluetooth smart 4.0 HF belt. It connects instantly, but always shows 0 bpm. With other apps (e.g. bkool), the heart rate is displayed correctly, so I guess it’s not the fault or e defect of the belt.
It is a Powrx Bluetooth low energy HF belt.
Hey Beau, sorry to hear Zwift is not connecting your with your HF belt. 
Can you try troubleshooting your pairing connection with our guide here? https://support.zwift.com/en_us/adding-a-heart-rate-monitor-before-a-ride-BkF2qSccm
If that doesn’t help feel free to send our technical support team a support conversation: Contact Us
They’ll help you out as soon as possible !