> ## Documentation Index
> Fetch the complete documentation index at: https://docs.avok.xyz/llms.txt
> Use this file to discover all available pages before exploring further.

# Sponsorship

> Avok's sponsored rail is a token paymaster: the user pays the fee in a token, and you bring your own infrastructure.

Avok can send transactions whose fee the user pays in an **ERC-20 token or SPL mint** instead of
the chain's native gas asset. Be precise about what "sponsored" means here, because the word is
overloaded across the ecosystem.

## A token paymaster, not a verifying paymaster

Avok's sponsored rail is a **token paymaster**: the user holds a paymaster-supported token, the
fee is charged in that token, and the paymaster and bundler collect it and pay the chain in native
gas on the user's behalf. The user still pays, just not in a currency they may not hold.

It is **not** a verifying paymaster, where an operator absorbs the fee and the user pays nothing.
A fee token is therefore required to reach this rail: the token *is* the payment. A send with no
fee token has nothing to charge, so it is self-pay by definition. An operator who wants to absorb
the cost does that as a policy at their own paymaster; from the SDK, the call is identical.

## Bring your own infrastructure

There is no default bundler, no default paymaster, and no default Kora endpoint, and there never
will be. A sponsored send is reachable only through a URL or a client you pass in. Supply nothing,
and every send is self-pay. That is the default posture, not a failure mode.

The reason is trust. Whoever runs the paymaster sees every sponsored transaction before it lands
and decides whether to relay it. A default endpoint would silently make that party a dependency of
every app that never configured one, and a counterparty the user never agreed to.

* **EVM** needs an ERC-4337 `bundlerUrl` (EntryPoint v0.8) **and** an ERC-7677 `paymasterUrl`,
  together. With only one, the chain falls back to self-pay.
* **Solana** needs a single `koraUrl`. Kora is both the fee payer and the submitter.

See [Sponsor EVM sends](/guides/sponsor-evm) and [Sponsor Solana sends](/guides/sponsor-solana).

## The fee token is per-send

A fee token is a payment the user makes, so a wallet must not choose one on their behalf. There is
no client-level default fee token; you pass it per send. Omit it, and the send is self-pay.

By default, asking for a fee token on a chain with no bundler and paymaster **degrades silently to
self-pay**. That lets one codebase sponsor on the chains where infrastructure exists and pay
natively on the ones where it does not, without branching. If your product promises users they can
pay fees in a token, set `requireSponsorship: true`, and a fee-token send that cannot reach the
sponsored rail throws before anything is signed, naming which side is missing.

## Check which rail ran

Every receipt carries `rail`, either `"sponsored"` or `"self-pay"`. It is the only thing that
tells you which path actually ran. If your app promises gasless transactions, check it rather than
assuming your configuration took effect. See [Receipts](/reference/receipts).

For the complete contract, including the custom `Bundler`, `Paymaster7677`, and `KoraClient`
interfaces, read `SPONSORED.md` in `@avokjs/core`.