Relayer & Subsidies Changelog - v7.4 to v8.0

This page covers changes to the Relayer pallet (subsidies, fee-paying keys) and the relay_tx call, which moves from Utility to Relayer. It is part of the v7.4 → v8.0 changelog.

Audience: anyone subsidizing accounts' transaction fees, or relaying signed calls on behalf of another account.

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Overview

In v7.4, granting a subsidy went through the generic Identity authorization system: set_paying_key created an AddRelayerPayingKey authorization, which the user key then accepted via accept_paying_key(auth_id) — the same generic accept/reject/consume mechanism used for key rotation, ownership transfers, and other authorization types.

In v8, subsidies get a dedicated state machine, native to the Relayer pallet: approve_subsidy writes directly into a new PendingSubsidies storage, and the user accepts with accept_subsidy(paying_key) — no authorization ID involved.

relay_tx also moves from Utility to Relayer in v8, gaining an expires_at field alongside the nonce mechanism it already had.

Breaking changes

1. Subsidy grant/accept flow replaced

v7.4	v8.0	Notes
set_paying_key(user_key, polyx_limit)	approve_subsidy(user_key, polyx_limit)	Renamed. No longer creates an Identity authorization — writes directly to PendingSubsidies
accept_paying_key(auth_id: u64)	(removed)	Replaced by accept_subsidy below
—	accept_subsidy(paying_key)	New. User accepts by naming the paying key directly, no auth_id
—	revoke_subsidy(user_key)	New. Subsidizer cancels a pending (not yet accepted) subsidy
remove_paying_key(user_key, paying_key)	remove_subsidy(user_key, paying_key)	Renamed, signature unchanged. Callable by either party, same as v7.4

update_polyx_limit, increase_polyx_limit, and decrease_polyx_limit are unchanged in name and signature — only their call indices shift, because of the two new calls inserted before them.

2. relay_tx moves from Utility to Relayer, and gains an expiry

// v7.4 - Utility::relay_tx
relay_tx(target: AccountId, signature: OffChainSignature, call: UniqueCall<RuntimeCall>)
// UniqueCall wraps the call with a nonce the caller must supply, checked against Utility's Nonces storage

// v8.0 - Relayer::relay_tx
relay_tx(target: AccountId, signature: OffChainSignature, call: Box<RuntimeCall>, expires_at: Moment)
// The nonce is no longer a caller-supplied argument -- it's tracked server-side in the new
// Relayer::RelayTxNonces storage (auto-incremented per target) and mixed into the signed
// message alongside expires_at

Utility::relay_tx and its Nonces storage are removed entirely, replaced by Relayer::relay_tx and the new RelayTxNonces storage. Replay protection is still nonce-based underneath, but the nonce is no longer an explicit call argument you supply and check yourself — it's resolved from chain state when building the signed payload, and expires_at is a new, separate expiry check on top. Either way, signed relay payloads built for v7.4 will not work on v8 — the call moved pallets and the payload shape changed.

3. Events renamed and retyped

v7.4	v8.0
AuthorizedPayingKey(EventDid, AccountId, AccountId, Balance, u64)	ApprovedSubsidy { user_key, paying_key, initial_polyx_limit }
AcceptedPayingKey(EventDid, AccountId, AccountId)	AcceptedSubsidy { user_key, paying_key, initial_polyx_limit }
RemovedPayingKey(EventDid, AccountId, AccountId)	RemovedSubsidy { user_key, paying_key, remaining }
UpdatedPolyxLimit(EventDid, AccountId, AccountId, Balance, Balance)	UpdatedPolyxLimit { user_key, paying_key, remaining, old_remaining }

All v8 events drop the identity field that every v7.4 event carried, and use named struct fields instead of positional tuples.

4. New events

RemovedPendingSubsidy { user_key, paying_key, initial_polyx_limit } (fired by revoke_subsidy), SubsidyDebited { user_key, paying_key, amount } (fired when a subsidized transaction consumes POLYX from the subsidy), RelayedTx { caller, target, result } (fired by relay_tx).

5. Errors changed

Removed: UserKeyCddMissing, PayingKeyCddMissing (no CDD requirement in the new flow), NotAuthorizedForPayingKey, NotAuthorizedForUserKey, BadAuthorizationType, IdentityNotFound (all specific to the old authorization-based flow).

New: NoPendingSubsidy (returned by accept_subsidy/revoke_subsidy when there is nothing pending), InvalidSignature and ExpiredRelayTx (both for relay_tx).

Unchanged: NoPayingKey, NotPayingKey, Overflow.

On Utility: InvalidSignature, TargetCddMissing, and InvalidNonce are removed along with relay_tx itself. UnableToDeriveAccountId remains, used elsewhere in Utility.

6. AuthorizationType::AddRelayerPayingKey renamed to OldAddRelayerPayingKey

The Identity pallet's AuthorizationData variant used by the old flow is renamed, not removed — this preserves the ability to decode pre-upgrade authorizations still sitting in storage. New code should not create this authorization type; use approve_subsidy instead.

Migration checklist

1. Replace set_paying_key with approve_subsidy and remove_paying_key with remove_subsidy (same arguments).
2. Replace accept_paying_key(auth_id) with accept_subsidy(paying_key) — stop tracking or waiting on an authorization ID for subsidy acceptance.
3. If you cancel subsidies before acceptance, use the new revoke_subsidy.
4. Move any relay_tx usage from Utility to Relayer, add an expires_at value when building the signed payload, and stop supplying a nonce yourself — it's now resolved from Relayer::RelayTxNonces rather than being a call argument.
5. Update event decoding for the new named-field shapes and the identity field removal; handle the new RemovedPendingSubsidy and SubsidyDebited events if you track subsidy lifecycle or spend.
6. Remove handling for CDD-related and authorization-related Relayer errors that no longer exist; add handling for NoPendingSubsidy, InvalidSignature, ExpiredRelayTx.

For the complete literal list of every added/removed/modified call, event, error, storage item, and constant on Relayer and Utility, see the Full Pallet API Reference.