Doctor refusing catecholamine testing. What should I do?

I finally found a cardiologist who informally diagnosed me with POTS. I’ve been on an extended release propranolol for a week which has helped though i still get post prandial spikes. I’ll be doing a TTT in a week or so but when I asked about catecholamine testing, the doctor mentioned they don’t have the facilities to do it. I’m pretty sure i have hyperPOTS but I *really* want to nail down the root cause for the sudden onset of symptoms. If I know what’s causing the tachycardia i can look for more targeted solutions.

Any idea how i can convince the doctor that the test is crucial to me getting better? She’s the first doctor who has actually acknowledged pots and is offering help so i also don’t want to piss her off lol.