Hi Hans,
You need BLE bluetooth. This is version 4 of bluetooth. If it’s an old Ipad maybe that’s why it doesn’t work.
The treadmill should not be connected before you start Zwift. Turn off the treadmill.
In order, turn on the iPad, launch Zwift then turn on the treadmill and go to app mode and press start. The treadmill should be recognized immediately in Zwift.
On your pc the 1st time you have to pair the treadmill in the bluetooth settings of windows with the 6-digit code. Then you launch Zwift.
The most important thing is really at least bluetooth 4 BLE.
Thierry