Every transaction on the Ethereum network requires Ether as a payment method for network fees. If you want only to send tokens it still requires Ether. Tangany has developed a solution called Gas Tank for such wallets, that only store tokens without any Ether. 

The Gas Tank fuels up the wallet that wants to send a token transaction by prefilling it. That allows transactions from any wallet (that is located within the client's Key Vault) without the hurdles of network fees. Clients can decide for every transaction whether the Gas Tank shall be used. 

If the Gas Tank is activated, our system defines the current fee situation on the market in order that the transaction is executed within a few blocks. You are able to speed things up/down via the configuration (also in the header of the transaction). The sender's wallet will then be deposited with the required amount of Ether in order to fulfill the transaction. There might be a bit of Ether dust left after the transaction on the sender's wallet.

The cumulated monthly consumption will be added to the monthly invoice.