Hello @zhak,
If you set the BTC withdrawal fee on the CoinPayments adapter to 40k then this is the fee paid to CoinPayments. This goes to pay the blockchain transaction and a portion is retained by CoinPayments for providing the wallet hosting service. If you were to set the fees to a higher amount, then the rest would remain with your site’s hot wallet. For example, if you set the fees to 50k, then 10k satoshis remain on your site’s hot wallet.
The deposit fee is 0.5%, as imposed by the platform. For more information please see: https://www.coinpayments.net/supported-coins
The CoinPayments platform is provided as a convenience. If you really care about controlling the fees you can set up a full node. However, you would also need to consider the cost of running – and maintaining – a full node wallet into your business plan.
Hope this helps.
with regards