[Question] where does the fund of the `rewards_account` comes from?

[boundless-forest]

pub struct PayRewardFromAccount<T, Relayer>(PhantomData<(T, Relayer)>);

impl<T, Relayer> PayRewardFromAccount<T, Relayer>
where
	Relayer: Decode + Encode,
{
	/// Return account that pays rewards based on the provided parameters.
	pub fn rewards_account(params: RewardsAccountParams) -> Relayer {
		params.into_sub_account_truncating(b"rewards-account")  // here
	}
}

There was a relayer_acount which was very similar to the rewards_account in the latest version. The user pays the cross-chain message fee to the relayer account when sending a message, after the message delivery proof is submitted to the source chain, this account pays the rewards to the message relayer and the confirmation relayer.

In the current code, I find that the repayer pallet are responsible for paying rewards with the rewards_account, this is the same with previous version. but I did not find where the fund of this account comes from. I guess the cross-chain fee might could be charged in the XCM layer or executor. If so, the rewards_account should be injected or configured in somewhere at runtime, but I have not found it.

[acatangiu]

Relayer rewards are paid from sovereign accounts (on source BH) of source/origin parachain. You can find more details at Who is Rewarding Relayers.

Our current plan for user fees is to have them disconnected from relayer rewards. Ongoing discussion here #2434.

[boundless-forest]

Relayer rewards are paid from sovereign accounts (on source BH) of source/origin parachain.

When and where will the sov account transfer the funds to the rewards_account? off-chain manual?

[acatangiu]

The "rewards_account" for relayers servicing ParaA->ParaB lane is the sovereign account of ParaA on BridgeHubA.

E.g. for Statemint->Statemine XCM message: Statemint will hold and fund sovereign accounts on BHP and BHK.

Statemint ---xcm(ExportMessage(inner_xcm))--> BridgeHubPolkadot ---relay(inner_xcm)--> BridgeHubKusama ---xcmp_dispatch(inner_xcm)--> Statemine
^                                             ^                                                   ^ 
|                                             |                                                   | 
user pays fee on extrinsic here,              |                                                   |
fee goes to Statemint treasury                |                                                   relayer gets "KSM tx fees refund" here for submit_message_proof()
                                              |                                                   from StatemintSovereignAccountOnBHK
                                              relayer gets "DOT tx fees refund" + "DOT reward"
                                              for submit_message_delivery_proof()
                                              from StatemintSovereignAccountOnBHP

Statemint treasury will periodically fund StatemintSovereignAccountOnBHP and StatemintSovereignAccountOnBHK

And everything is mirrored for the other direction.