I have an account at a prop shop. I have been using one of the trading platforms they offer and I have been paying for market data. Now I want to try a second platform that by the way will feed the same account (while still using the first one). Do I have to pay for market data again, or since its for the same person same account I shouldn't pay a second time. Thank you
YES. You will have to pay for market data for each platform. They will require their own data feed. Even on the same computer.
The easy answer is "it depends on the platform". I have more than one Bloomberg terminal, I subscribe to NYSE data and I only pay the NYSE once for data however I pay Bloomberg for two terminals. Some places (like retail brokers) do not have the ability to charge or not charge for data - so you are on the hook no matter what. Other places integrate the data into a "platform fee" so you will get the data free with the XXX per month platform fee. It depends on your platform but the exchanges do not double charge for feeds.
With your proof of payment for the existing data feed, try asking for a waiver to avoid paying for that same data feed twice.