Watch any YouTube video review of the products Fitbit sells and you would’ve known that before you bought it. Its a problem with wrist worn HR devices. If you want accurate, get a chest strap, otherwise deal with the fact that its not perfectly accurate. I’m sure its closer than you’d get without a HR monitor…

Wrist monitors are inherently inaccurate. I did a bit of reading before I got my HR, so my expectations weren’t that high. If you want accurate, get a Polar chest strap.