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Sponsorship Models

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DEVELOPER_SPONSORS

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How it works

1. Developer builds any Stacks contract call with sponsored: true
2. User signs the transaction (no STX needed)
3. velumx.sponsor(signedTxHex) — relayer co-signs and broadcasts
4. On-chain: the contract call executes, relayer pays STX gas

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No paymaster contract needed

// Call any Stacks contract, gaslessly
const tx = await buildSponsoredContractCall({
  contractAddress: 'SPQC38PW542EQJ5M11CR25P7BS1CA6QT4TBXGB3M',
  contractName: 'stableswap-stx-ststx-v-1-2',
  functionName: 'swap-x-for-y',
  functionArgs: [...],
  publicKey: userPublicKey,
});
const { txid } = await velumx.sponsor(await wallet.sign(tx));

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Best for

• Zero-friction onboarding (day-0 users with empty wallets)
• Subsidized DeFi experiences
• Any protocol action — unlimited coverage

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USER_PAYS

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How it works

1. Developer deploys their own paymaster contract (copy velumx-defi-paymaster-v1 as template)
2. User signs a transaction calling the paymaster
3. velumx.sponsor(signedTxHex) — relayer co-signs and broadcasts
4. On-chain: paymaster collects fee → executes action (atomic rollback if action fails)

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Developer owns the paymaster

• Full control over what actions are supported
• No dependency on VelumX contract upgrades
• Immutable once deployed — no admin key risk

// Call your own paymaster contract
const tx = await buildSponsoredContractCall({
  contractAddress: 'SP...my-paymaster',
  contractName: 'my-protocol-paymaster-v1',
  functionName: 'swap-with-fee',
  functionArgs: [
    /* swap params */,
    uintCV(BigInt(estimate.maxFee)),
    principalCV(estimate.relayerAddress),
    /* fee-token trait */,
  ],
  publicKey: userPublicKey,
});
const { txid } = await velumx.sponsor(await wallet.sign(tx), {
  feeToken: 'SP...aeusdc',
  feeAmount: estimate.maxFee,
});

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Best for

• Sustainable fee models where users pay in the token they hold
• Protocols where users already have stablecoins (aeUSDC, USDCx)
• Revenue generation — developer earns markup on every transaction

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Comparison

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High-Impact Use Cases