As far as I know, Zerodha shares are sold based on -
The shares you purchase first are considered to be sold first from your account.
What rule does AngelOne follows?
To the best of my knowledge every broker has to follow fifo method. This method is used to compute capital gain as well. Hence the rule should be universal to all brokers.
When a security gets credited into your demat account they all become equal. Let’s say you buy 1 share of Reliance (for example) on 1 March and another share on 3 March. There’s no tag to identify which share of Reliance was bought on 1 March which on 3 March. You just end up with 2 shares of Reliance in your demat.
FIFO is a methodology everyone has to follow to compute taxable income. If your broker gets the calculation wrong it’s not their responsibility. I expect Angel follows FIFO methodology as well to calculate taxable income because that is the correct way. In the above example if you then sell one share of Reliance you have to assume the that the share you sold was the one you bought on 1 March. You can deduct all the charges from your gross PnL to calculate the net PnL.