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When you hold customer funds in Bitnob Enterprise wallets, every outbound transfer needs native gas at the sending address. With one wallet per customer, keeping ETH or TRX at thousands of addresses quickly becomes unmanageable. A gas station solves this: one balance of the native asset per chain, which pays the fee for any sponsored transfer from your wallets.

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The model

A gas station belongs to your organization and works on one chain. It has its own on-chain address, holding the chain’s native asset (asset is ETH, TRX, and so on). When you send from one of your wallets with sponsorship on, the gas station pays the network fee. The sending wallet only needs the token it is sending.

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Sponsoring a transfer

Set sponsor: true on Create transaction:
The transaction response shows the sponsorship: To see what sponsorship will cost before you send, pass the same sponsor: true to Estimate transaction fee. Sponsored transactions still pass through your policies. Sponsorship changes who pays the fee, not whether the transfer is allowed.

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Thresholds and auto-refill

Each gas station has a threshold in the native asset’s display unit, for example "0.05" ETH. It drives two things:
  • Health. health_status is healthy while the balance is at or above the threshold, and low below it.
  • Auto-refill. With auto_refill_enabled, when the balance drops below threshold, the gas station pulls refill_amount from refill_from_wallet_id, a wallet you choose, usually a treasury wallet on the same chain.
You can also top up at any time with Refill gas station. A refill is an ordinary transaction from the source wallet, so it is subject to your policies and appears in your transaction history.
Auto-refill moves funds out of the source wallet, so that wallet needs enough native balance too. If both run dry, sponsored transfers on that chain stop. Watch the source wallet as well as the gas station.

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Alerts

Gas stations emit three webhook events: Route critical_balance to whoever can fund the source wallet. A run of auto_refilled events at short intervals means refill_amount is too small for your volume.

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Units

Gas station fields come in two forms. threshold and refill_amount are display-unit decimals, such as "0.25" ETH, with _raw versions in base units. balance is only in base units, such as wei or sun. Divide it by 10^asset_decimals before you compare it with threshold.

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Sponsoring externally signed Tron transactions

A gas station can also pay for a Tron transaction your system didn’t sign through Bitnob. Sponsor and broadcast takes the signed raw transaction, funds the fee from the gas station, and broadcasts it. The response includes the sponsor_tx_id of the fee-funding transaction and the amount sponsored in TRX.

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Gas stations or sponsored transfers

If you run both custodial and self-custody flows, you can use both. See How sponsored transfers work.