Hi T. Janne,
I checked the full “in-development” list of supported devices HERE on the Zwift Android Beta Feedback forum thread and regrettably, I don’t see that the Bv9500 is currently listed as a supported device. That may be the reason why you’ve had some troubles pairing your Tacx smart trainer to the app.
If you’ve never used your particular Tacx trainer with Zwift before, I’d also recommend double checking our list of supported trainers on the hardware page to make sure your trainer is supported for use with Zwift.