Cashback is calculated according to the Cashback Table in the FBS Trader application.
In the table above, you see the cashback paid for 1 lot. Thus, to calculate the final cashback, you need to multiply this amount by the number of lots.
E.g., your cashback level percentage is 5% and you have traded 2.3 lots on AUDUSD. This means that your cashback for this order will be as follows: 2.3 * 0.05 = $0.11
For stocks, the cashback amount depends on the current price of the stock. When trading stocks a fixed commission from the price is deducted (you can check the commission amount in the stock info).
Thus, the cashback for stocks is calculated according to the following formula:
stock commission * (cashback level percentage / 100) * order volume
E.g., you are buying Disney stock, and its current buy price is 169.33. The commission for the Disney stock is 0.35%, i.e., $0.59 for 1 stock lot. You have opened a 3 lot order and your cashback level percentage is 5%. This means that your cashback for this order will be as follows: 0.59 * (5/100) * 3 = $0.08 (8 cents).
For every lot traded with a hedge, you get 50% of the Cashback credited for 1 standard lot.
E.g., you have 10% Cashback and trade EURUSD. According to "Cashback table", the cashback for the instrument is $1 per lot. You trade with a hedge, i.e., open a 2 lot buy order and a 2 lot sell order simultaneously. When you close these orders, you will get a $2 Cashback.
For every stock lot traded with a hedge, you get 25% of the Cashback credited for 1 stock lot.
E.g., you are buying 2 Disney stock lots and selling 2 Disney stock lots simultaneously. Your cashback level percentage is 20%. The current Disney stock buy price is 169.33 and sell price is 169.26. The commission for the Disney stock is 0.35%, i.e., in this case, $0.59 for 1 stock lot (either buy or sell). Thus, your cashback for all 4 orders would have been as follows: 0.59 * (20/100) * 4 = $0.47
But since you have used hedging, you will get 25% of this cashback amount ($0.11).
Cryptocurrency and bonus funds
Cashback is not paid for the trading on bonus funds (e.g., you cannot get cashback for trading on Quick Start Bonus funds, but you will get cashback as soon as you transfer your profit to a real account and start trading on it).
Cashback is not paid for trading on cryptocurrency, though the lots traded on it are taken into account for the next Cashback level calculation (1 lot traded on cryptocurrency = 0.01 standard lot).