Candide Solana Paymaster: pay gas in USDT — zero SOL transfers via Kora

Candide Solana Paymaster: pay gas in USDT so accounts with zero SOL can still send SPL transfers. It is Candide’s first non-EVM product — a hosted Kora endpoint that cosigns as fee payer, fronts SOL for fees and rent, and collects the equivalent in USDT inside the same transaction.

Announcement: docs.candide.dev/blog/solana-paymaster. Guide: Pay Gas in USDT on Solana. RPC ref: Solana Paymaster RPC methods. Dashboard: dashboard.candide.dev. X: @candidelabs.

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The problem

Stablecoin users hold USDT/USDC, not SOL. On Solana an account with balances but no native SOL cannot pay fees or create ATAs — so wallets bounce people to an exchange mid-funnel. EVM teams solved this with ERC-4337 token paymasters; Candide’s Solana answer reuses that product intuition on Foundation’s open fee-payer standard: Kora.

Important distinction: this is not a proprietary proprietary SDK lock-in. Because the service speaks Kora JSON-RPC, any Kora client can target it — including @solana/kora and Tether’s Wallet Development Kit gasless Solana package.

How it works

User wallet (may have 0 SOL, has USDT)
   │  builds SPL transfer + USDT fee ix to payment_address
   │  user signs (not as fee payer)
   ▼
Candide Solana Paymaster (hosted Kora)
   │  validates policy
   │  cosigns as fee payer (signer_address)
   │  submits tx
   ▼
Solana
   • fee payer spends SOL (fees + rent)
   • user pays fee_in_token USDT in same tx

Fee is priced from the live SOL cost of the transaction. If the recipient lacks a USDT ATA, rent to create it is folded into the quoted USDT fee.

Endpoint and auth

https://api.candide.dev/api/v3/solana/YOUR_API_KEY

# or key in header:
https://api.candide.dev/api/v3/solana
Header: x-api-key: YOUR_API_KEY

# smoke test
curl https://api.candide.dev/api/v3/solana/YOUR_API_KEY \
  -H "Content-Type: application/json" \
  -d '{"jsonrpc":"2.0","id":1,"method":"getPayerSigner","params":[]}'

Get the key from the Candide dashboard. Keep the URL secret — it embeds the key when using path style.

Fast path: Tether WDK

Packages (versions as verified in Candide’s guide): @tetherto/[email protected], @solana/[email protected].

npm install @tetherto/wdk-wallet-solana-gasless @solana/kora

import WalletManagerSolanaGasless from "@tetherto/wdk-wallet-solana-gasless"
import { KoraClient } from "@solana/kora"

const nodeUrl = process.env.SOLANA_NODE_URL!
const paymasterUrl = process.env.SOLANA_PAYMASTER_URL! // Candide URL+key
const usdtMint = "Es9vMFrzaCERmJfrF4H2FYD4KCoNkY11McCe8BenwNYB"

const kora = new KoraClient({ rpcUrl: paymasterUrl })
const { signer_address: paymasterAddress } = await kora.getPayerSigner()

const wallet = new WalletManagerSolanaGasless(seedPhrase, {
  provider: nodeUrl,
  paymasterUrl,
  paymasterAddress,
  paymasterToken: { address: usdtMint },
  transferMaxFee: 1_000000n, // abort if fee > 1 USDT
})

const account = await wallet.getAccount(0)

// quote (USDT base units, 6 decimals)
const quote = await account.quoteTransfer({
  token: usdtMint,
  recipient,
  amount: 100000n, // 0.1 USDT
})

// send — user never needs SOL
const result = await account.transfer({
  token: usdtMint,
  recipient,
  amount: 100000n,
})
// result.hash, result.fee

Full runnable sample: candidelabs/tether-wdk-candide …/01-usdt-gas.

Raw Kora RPC flow

If you are not on WDK, the documented flow is:

1. getPayerSigner → set signer_address as fee payer; fee goes to payment_address.
2. Build the tx (or use paymaster transferTransaction).
3. estimateTransactionFee → fee_in_token.
4. Append an SPL transfer of fee_in_token to payment_address as the last instruction; re-estimate until stable (usually one iteration).
5. User signs → signAndSendTransaction (or signTransaction + your RPC).

Conventions differ from Candide’s EVM paymaster: Solana txs are base64 wire format; amounts are decimal base units; request params are named objects; response fields are snake_case.

Note: Kora’s newer getPaymentInstruction is not enabled on this endpoint (returns -32600). Build the fee payment as a plain SPL transfer.

Tokens and sponsorship modes

Live allowlist: getSupportedTokens. Default mode is token gas payment inside the same transaction — not free gas unless sponsorship is enabled for your key.

Policy limits (read before you integrate)

From the RPC reference “Current Policy” (as documented — re-check getConfig in production):

• Only tokens enabled for your endpoint (as fee mint and transfer mint).
• Fee payment must be present and sufficient or sign/send rejects.
• Only five programs may be invoked: System, SPL Token, ATA, Compute Budget, Address Lookup Table. Token-2022 is not allowed yet.
• Fee payer spends at most 9,000,000 lamports per tx (fees + rent).
• Max 10 signatures; durable nonce txs rejected.

That program allowlist means this is a stablecoin transfer paymaster today, not a general “sponsor any dapp ix” relayer. Complex DeFi menus still need a custom Kora operator or self-hosted policy.

Where it sits vs Kora DIY

Read the Foundation-side design in Kora: fee abstraction so users never need SOL for gas.

Roadmap signal

Candide’s post: mainnet USDT is the only fee token by default today; sponsored transactions (app pays, user pays nothing) are next — mirroring their EVM InstaGas product. Contact for USDC/other tokens and sponsorship enablement.

Builder checklist

1. Create Candide dashboard key; store paymaster URL server-side.
2. Decide WDK transfer() vs raw Kora client.
3. Enforce transferMaxFee / quote ceilings in UX.
4. Confirm recipient ATA creation rent is acceptable in the USDT fee.
5. Do not promise Token-2022 or arbitrary program calls until policy expands.
6. Production RPC: paid Solana provider; poll signatures if you need confirmed finality beyond submit.

Resources

• Launch post
• Pay Gas in USDT guide
• RPC methods
• Example repo
• Solana Kora docs · DevRels Kora article
• Tether WDK
• Candide on DevRels

Bottom line

Candide Solana Paymaster is the practical “pay gas in USDT” button for Solana stablecoin UX: hosted Kora, standard clients, WDK one-call transfers. Scope it correctly — SPL Token path, USDT default, strict program allowlist — and it removes the SOL chicken-and-egg for the most common wallet action. For custom fee tokens or broader ix sets, run your own Kora policy or wait for Candide’s sponsorship/token expansions.