how often does binance refund fees in the margin account?

API Spot/Margin API
1

I am making buy orders in the isolated margin account. I have BNB burn toggled for paying fees, so my understanding is that:

  1. the fees are first paid in the base asset when the trade is executed, e.g. in BTC when buying 100$ in the BTCUSDT isolated account
  2. the same fees are then paid with BNB in the spot account, assuming there is enough
  3. the first fees are refunded in the isolated account at a later stage.

Is there any documentation that explain when step 3 occurs?

Thanks