Every transaction on the Ethereum network requires Ether as a payment method for network fees. Tangany has developed a solution called Gas Tank for users who want to mitigate the manual handling of Ether on their wallets for certain use cases (e.g., tokens. 

Find more information in the Custody API docs: https://docs.tangany.com/docs/tangany-custody-api/ay1339exoa0xd-concepts#gas-tank