Pay server - is the blockchain microservice which is working on zigzag.io. It is used as unified API for other microservices to receive and send cryptocurrency.

State	Feature
implemented	Unify payment API for BTC, LTC, DASH, ETH, BCH, and Lightning Network
implemented	Report health statistics about internal state of synchronisation, fees, request delays, sent and received volume, amount of fees spent on payments
not implemented	Payment re-try in case of failure
not implemented	UTXO re-orginisation
not implemented	Lightning Network channel re-balancing
not implemented	Support of payments on HTLC addresses

GRPC API:

    // CreateReceipt is used to create blockchain deposit address in
    // case of blockchain media, and lightning network invoice in
    // case of the lightning media, which will be used to receive money from
    // external entity.
    rpc CreateReceipt (CreateReceiptRequest) returns (CreateReceiptResponse);

    // ValidateReceipt is used to validate receipt for given asset and media.
    rpc ValidateReceipt (ValidateReceiptRequest) returns (EmptyResponse);

    // Balance is used to determine balance.
    rpc Balance (BalanceRequest) returns (BalanceResponse);

    // EstimateFee estimates the fee of the payment.
    rpc EstimateFee (EstimateFeeRequest) returns (EstimateFeeResponse);

    // SendPayment sends payment to the given recipient,
    // ensures in the validity of the receipt as well as the
    // account has enough money for doing that.
    rpc SendPayment (SendPaymentRequest) returns (Payment);

    // PaymentByID is used to fetch the information about payment, by the
    // given system payment id.
    rpc PaymentByID (PaymentByIDRequest) returns (Payment);

    // PaymentsByReceipt is used to fetch the information about payment, by the
    // given receipt.
    rpc PaymentsByReceipt (PaymentsByReceiptRequest) returns (PaymentsByReceiptResponse);

    // ListPayments returnes list of payment which were registered by the
    // system.
    rpc ListPayments (ListPaymentsRequest) returns (ListPaymentsResponse);