Fit bit not syching with phone

Having enjoyed Fitbit watches for a few years I stopped using them. The reason was that once Fitbit demanded you had to go through Google to synch it it just didn’t work. Then Ifound I could on a couple of occasions go through Fitbit. Wonderful until it stopped and a message that I was now with Google appeared so once again no synchronisation. I now use a normal watch and I see how many steps I have done on my iPhone in the already installed health app -the one with a heart on it.

It took 2 weeks for my watch to start talking to my app, but it only connects when I open the app. So yesterday I was busy and never opened it. So apparently I stayed in bed all day. Not one step
When this watch goes, I'll buy into a totally different set-up. Google Health has destroyed Fitbit

I have the Sense 2..that went across OK. Perhaps let the battery drain, recharge then boot it up manually, see if that fixes it?

I have Charge 6 fit bit, since it became Google Health cannot get data as previously.
Where am I going wrong ?
Pkease help!