The pay module is the base transactional layer of the Terra blockchain: it allows assets to be sent from one Account to another. It reads the currently effective tax-rate and tax-cap parameters from the treasury module to enforce a stability layer fee.



// MsgSend - high level transaction of the coin module
type MsgSend struct {
FromAddress sdk.AccAddress `json:"from_address"`
ToAddress sdk.AccAddress `json:"to_address"`
Amount sdk.Coins `json:"amount"`

The pay module can be used to send coins from one Account to another. A MsgSend is constructed to facilitate the transfer. If the balance of coins in the Account is insufficient or the recipient Account does not exist, the transaction fails.

Multisend via batching

// MsgMultiSend - high level transaction of the coin module
type MsgMultiSend struct {
Inputs []Input `json:"inputs"`
Outputs []Output `json:"outputs"`

The pay module can be used to send multiple transactions at once. Inputs contains the incoming transactions, and Outputs contains the outgoing transactions. The coin balance of the Inputs and the Outputs must match exactly. Batching transactions via multisend has the benefit of conserving network bandwidth and gas fees.

If any of the Accounts fails, then taxes and fees already paid through the transaction is not refunded.


Gas fees

As with any other transaction, MsgSend and MsgMultiSend has to pay a gas fee the size of which depends on validator's preferences (each validator sets his own min-gas-fees) and the complexity of the transaction. Notes on gas and fees has a more detailed explanation of how gas is computed. Important detail to note here is that gas fees are specified by the sender when the transaction is outbound.

Stability fees

Further to the gas fee, the pay module charges a stability fee that is a percentage of the transaction's value. It reads the tax-rate and tax-cap parameters from the treasury module to compute the amount of stability tax that needs to be charged.

  • tax-rate: an sdk.Dec object specifying what % of send transactions must be paid in stability fees

  • tax-cap: a cap unique to each currency specifying the absolute cap that can be charged in stability fees from a given transaction.

For an example MsgSend transaction of 1000 usdr tokens,

stability fee = min(1000 * tax_rate, tax_cap(usdr))

For a MsgMultiSend transaction, a stability fee is charged from every outbound transaction.

Unlike with the gas fee which needs to be specified by the sender, the stability fee is automatically deducted from the sender's Account.