Charge 5 - Find phone feature doesn’t work.

[Mustrideorski]

I’ve only had my Charge 5 one week. The find phone feature worked once the first day. Two days later I tried again and it didn’t work. 
I tried restarting my Fitbit and it worked once. 
Since then I can’t get it to work. Yes, I’ve restarted both the FitBit and the phone. 
Any suggestions appreciated. 

[KChumley]

I’ve learned that it only works when I have the Fitbit app open and running in the background.