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Cartridge Slot is a private, fee-free Katana chain forked from Starknet mainnet. It is purpose-built for games and high-throughput apps that need instant, zero-cost transactions. Cavos integrates with Slot so that users can execute transactions on the Slot chain without a paymaster — Katana runs with no_fee = true, so gas is always free.

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How It Works

  1. Account deployment on mainnet happens automatically after login(), as usual.
  2. First executeOnSlot() call lazily deploys the account on Slot and registers the session key. The SDK uses a relayer (configurable or default) to handle the execute_from_outside_v2 call needed for JWT verification.
  3. Subsequent executeOnSlot() calls use the session key directly — no relayer, no paymaster, just a direct invoke.

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Configuration

Add slot to your CavosProvider config: 
import { CavosProvider } from '@cavos/react';

export function Providers({ children }) {
  return (
    <CavosProvider
      config={{
        appId: 'your-app-id',
        network: 'mainnet',         // Target network state
        paymasterApiKey: 'your-key',
        slot: {
          rpcUrl: 'https://api.cartridge.gg/x/your-project/katana',
          chainId: '0x57505f4341564f53', // hex of internal chain ID
          relayerAddress: '0x...',       // Optional: funded account on Slot
          relayerPrivateKey: '0x...',    // Optional: its private key
        },
      }}
    >
      {children}
    </CavosProvider>
  );
}

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SlotConfig Options

PropertyTypeRequiredDescription
rpcUrlstringYesRPC URL of your Cartridge Katana Slot instance
chainIdstringOptionalChain ID for the Slot chain. Defaults to the primary network’s ID. You should provide the exact internal VM chain ID (e.g., 0x57505f4341564f53 for WP_CAVOS) to avoid signature mismatches.
relayerAddressstringOptionalAccount address to act as relayer for Slot deployment. Defaults to the built-in Cavos relayer.
relayerPrivateKeystringOptionalPrivate key for the relayer account.
[!WARNING] Important: Katana sequencers often report SN_MAIN via their RPC, but use a custom internal chain ID inside the Cairo VM. Because the Cavos session registration signature depends on this internal chain ID, you must manually set the chainId in your config to match the internal ID of your Katana genesis (e.g., WP_CAVOS / 0x57505f4341564f53). If you do not provide the correct internal chainId, you will encounter an “Invalid session key signature” error.
[!IMPORTANT] Address Parity: On Cavos Slots, the CavosAccount class and JWKSRegistry are typically deployed at the exact same addresses as production (Sepolia/Mainnet). The SDK now automatically uses these parity addresses. You no longer need to provide classHash or jwksRegistryAddress in the SlotConfig.
[!NOTE] If slot is not present in the config, nothing Slot-related happens — executeOnSlot() will throw.

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Finding your internal Katana Chain ID

Since you cannot rely on the RPC starknet_chainId method to give you the internal VM chain ID of your Slot or Katana node, you must query it directly from within the Cairo VM. You can do this by deploying a minimalistic Cairo contract that returns get_tx_info().chain_id: 
#[starknet::interface]
pub trait ICheckChainId<TContractState> {
    fn get_chain_id(self: @TContractState) -> felt252;
}

#[starknet::contract]
pub mod CheckChainId {
    use starknet::info::get_tx_info;

    #[storage]
    struct Storage {}

    #[abi(embed_v0)]
    impl CheckChainIdImpl of super::ICheckChainId<ContractState> {
        fn get_chain_id(self: @ContractState) -> felt252 {
            get_tx_info().unbox().chain_id
        }
    }
}
  1. Deploy the contract above to your Katana node using starkli.
  2. Call the get_chain_id function: 
    starkli call <contract_address> get_chain_id --rpc https://api.cartridge.gg/x/your-project/katana
  3. Use the exact hexadecimal result in your slot.chainId configuration array.

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Executing Transactions on Slot

Use executeOnSlot() instead of execute() to route transactions to the Slot chain: 
import { useCavos } from '@cavos/react';

function GameAction() {
  const { executeOnSlot, walletStatus } = useCavos();

  const handleMove = async () => {
    const txHash = await executeOnSlot({
      contractAddress: GAME_CONTRACT_ADDRESS,
      entrypoint: 'make_move',
      calldata: ['42', '7'],
    });

    console.log('Move submitted on Slot:', txHash);
  };

  return (
    <button onClick={handleMove} disabled={!walletStatus.isReady}>
      Make Move
    </button>
  );
}

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Multicall on Slot

const txHash = await executeOnSlot([
  {
    contractAddress: RESOURCE_CONTRACT,
    entrypoint: 'collect',
    calldata: [playerId],
  },
  {
    contractAddress: GAME_CONTRACT,
    entrypoint: 'upgrade',
    calldata: [buildingId, '1'],
  },
]);

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Session Policy on Slot

The session policy configured in CavosProvider (session.defaultPolicy) applies to both mainnet and Slot transactions. Configure allowedContracts to include your Slot game contracts: 
<CavosProvider
  config={{
    appId: 'your-app-id',
    network: 'mainnet',
    paymasterApiKey: 'your-key',
    session: {
      defaultPolicy: {
        allowedContracts: [
          GAME_CONTRACT_ADDRESS,    // Same address on Slot as mainnet
          RESOURCE_CONTRACT_ADDRESS,
        ],
        maxCallsPerTx: 10,
      },
    },
    slot: {
      rpcUrl: 'https://api.cartridge.gg/x/your-project/katana',
    },
  }}
>

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Differences from execute()

execute()executeOnSlot()
Target chainStarknet mainnet / sepoliaCartridge Slot (Katana)
GasSponsored by Cavos PaymasterFree (no_fee = true)
Paymaster neededYes (for sponsored)No
First call overheadNoneDeploys account + registers session on Slot
Subsequent callsDirect invoke or paymasterDirect invoke with session key

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Troubleshooting

SymptomLikely CauseFix
executeOnSlot throws “Slot not configured”slot key missing from configAdd slot: { rpcUrl: '...' } to CavosProvider config
First Slot transaction takes longDeploying account + registering sessionExpected on the very first call — subsequent calls are instant
”Invalid session key signature” on SlotMismatched Katana chain ID or SDK versionProvide the internal Katana chainId (e.g. 0x57505f4341564f53 for WP_CAVOS) in the slot config, and ensure @cavos/react is updated
Transaction rejected on SlotContract not in session policyAdd contract to allowedContracts in session.defaultPolicy
Wrong chain IDCustom Katana uses an internal VM chain ID different from RPCPass chainId explicitly in slot config