Please note that gas will be required to both send and receive payments through Tabby Pay, as each touch-point with the smart contract requires a new transaction on the blockchain.
For the time being, a small amount of gas will be required to send/receive any payments. If there is not enough balance available to cover the gas, the transaction will not complete.
In a future Ethereum update, it will be possible for smart contracts to pay gas on behalf of the user. Until then, the recipient will require a small amount of Ether to accept payment.