Fee System

Fee System

In the BTP system, a user pays for all message deliveries in the source chain COIN. The following table shows, how it's calculated.

Name	Actual Fee	Fee on ICON
ICON to ETH	706,938 Gwei	706938 / (10**9) * 1880 / 0.23 = 5.778449739130435 ICX
ETH to ICON	0.01 ICX	0.01 ICX

(Assuming that ICX is 0.23 USD and ETH is 1880 USD)

So, if it sends a one-way message from ICON to ETH, it should pay for 5.78 ICX. If it sends a two-way message for ICON to ETH, it should pay for 5.79 ICX.

The same thing happens on routed messages.

Fee Calculation in TestNet

We are using the following exchange rate for this BTP Test Net.

Network	COIN	Price(USD)
Ethereum2(Sepolia)	ETH	1880.00
ICON(Berlin)	ICX	0.26
BSC(Test)	BNB	322.00
HAVAH(BTP Test)	HVH	0.26

We referred actual price table of the market, but some of them were adjusted for easy usage.

And calculated fee for a message for each connection is following (We assume that 100 messages are delivered in a day)

Connection	Fee in USD	Fee in ETH(wei)
ICON -> ETH2(IE)	1.329043	706937800000000
ETH2 -> ICON(EI)	0.056664	30140466117021
BSC -> ICON(BI)	0.010569	5621579869681
ICON -> BSC(IB)	2.276340	1210818997872340
HAVAH -> ICON(HI)	0.005054	2688242686170
ICON -> HAVAH(IH)	0.005054	2688242686170

Fee for deliveries is calculated with the price and amount of transaction fees by the relays. The estimation logic could be changed at any time.

The example ETH fee table with the calculated values

Destination	List of Fee	Calculated
ICON	[ EI, IE ]	[ 30140466117021, 706937800000000 ]
BSC	[ EI, IB, BI, IE ]	[ 30140466117021, 1210818997872340, 5621579869681, 706937800000000 ]
HAVAH	[ EI, IH, HI, IE ]	[ 30140466117021, 2688242686170, 2688242686170, 706937800000000 ]

With this fee table, Fee for a one-way message to BSC from ETH is 30140466117021 + 1210818997872340 ⇒ 1240959463989361 wei(ETH). A similar algorithm can be applied for each chain.

Apply Fee

When we send a transaction, we also set the amount of the fee to be paid for executing the transaction. But BTP Fee is not collected through a standard fee aggregation system because it's not a part of the system framework, but a part of DApp. So it doesn't follow the rule of the normal transaction fee system.

It uses getFee() API to get an amount of fee to be paid while it sends a message. While it sends a message, it should provide the fee as value (transferring coin) along with a fee for executing the transaction. Even if you set a system fee limit high enough to pay BTP Fee ( setting a high gas_limit or step_limit ), it can't collect them.

So, if you see "Not Enough Fee" in the user exception(revert), you should set the proper transfer amount according to the value from getFee() method.

getFee() returns the amount of the fee for delivering a one-way or two-way message in its own local coin unit. So, if it returns 1240959463989361 in the Ethereum environment, it means 0.001240959463989361 ETH.