Jet black hrm

Hi. Any help welcomed.
I purchased the jet black hrm and I’m having trouble with it turning on. There’s a green light on it which I’m guessing is telling me it’s on and connecting. Once connected i have no issues just the amount of time i spend trying to get it on etc. Sometimes it’s instant others I’m trying different things for maybe 5 mins or more to get it to work. I have the hub one.
So no problems once it connects just getting it to turn on (get that green light on)
And i have tried changing battery
Thanks rich