Postural Orthostatic Tachycardia Syndrome (P.O.T.S.)

Mostly just want an answer to the question, but also want to rant a little, so here's my story. I got 'diagnosed' with POTS by my primary doctor who took my heart rate laying down for a minute, then standing up for a minute, and responded with "yikes". To get a real diagnosis I was supposed to get a TTT, but had to get a referral from the cardiologist first. In the meantime, I've been on a high salt diet and I got a fitbit to monitor my heart rate (I know apple watch is better but even the refurbished ones were too expensive). It has been helpful in seeing whenever I feel like shit, I can check my heart rate and it's usually in the 120-130s despite not doing anything more than standing up.

Today I went to see the cardiologist, told them my symptoms, etc., and they asked if my watch tracked my heart rate and what it was doing during my episodes. I told them, but then they realized it was a fitbit and said fitbits aren't accurate and I don't have POTS because I don't have the symptoms. They refused to give a referral for a TTT. They said it's probably high cholesterol or something and has recommended a no salt diet (which I will completely ignore because it's hard to stand up if I don't get enough salt).

Anyway, I didn't expect fitbit to be perfectly accurate, but I thought the readings were enough to be a concern. Does anyone know how inaccurate it really it?