Payment
A Payment transaction represents a transfer of value from one account to another. (Depending on the path taken, this can involve additional exchanges of value, which occur atomically.) This transactio
Example
Amount
Amount
The amount of currency to deliver. For non-XAH amounts, the nested field names MUST be lower-case. If the tfPartialPayment flag is set, deliver up to this amount instead.
Destination
String
AccountID
The unique address of the account receiving the payment.
DestinationTag
Number
UInt32
(Optional) Arbitrary tag that identifies the reason for the payment to the destination, or a hosted recipient to pay.
InvoiceID
String
Hash256
(Optional) Arbitrary 256-bit hash representing a specific reason or identifier for this payment.
Paths
Array of path arrays
PathSet
(Optional, auto-fillable) Array of payment paths to be used for this transaction. Must be omitted for XAH-to-XAH transactions.
SendMax
Amount
DeliverMin
[Currency Amount][]
Amount
(Optional) Minimum amount of destination currency this transaction should deliver. Only valid if this is a partial payment. For non-XAH amounts, the nested field names are lower-case.
Types of Payments
The Payment transaction type is a general-purpose tool that can represent several different types of abstract actions. You can identify the transaction type based on the transaction's fields, as described in the table below:
Payment type
Amount
SendMax
Paths
Address = Destination?
Description
Direct XAH-to-XAH Payment
String (XAH)
Omitted
Omitted
No
Transfers XAH directly from one account to another. Always delivers the exact amount. No fee applies other than the basic transaction cost.
Creating or redeeming tokens
Object
Object (optional)
Optional
No
Increases or decreases the amount of a non-XAH currency or asset tracked in Xahau. Transfer fees and freezes do not apply when sending and redeeming directly.
Cross-currency Payment
Object (non-XAH) / String (XAH)
Object (non-XAH) / String (XAH)
Usually required
No
Send tokens from one holder to another. The Amount or SendMax can be XAH or tokens, but they cannot both be XAH. These payments ripple through the issuer and can take longer paths through several intermediaries if the transaction specifies a path set. Transfer fees set by the issuer(s) apply to this type of transaction. These transactions consume offers in the decentralized exchange to connect between different currencies, or possibly even between currencies with the same currency code and different issuers.
Partial payment
Object (non-XAH) / String (XAH)
Object (non-XAH) / String (XAH)
Usually required
No
Sends up to a specific amount of any currency. Uses the tfPartialPayment flag. May include a DeliverMin amount specifying the minimum that the transaction must deliver to be successful; if the transaction does not specify DeliverMin, it can succeed by delivering any positive amount.
Currency conversion
Object (non-XAH) / String (XAH)
Object (non-XAH) / String (XAH)
Required
Yes
Special issuer Values for SendMax and Amount
Most of the time, the issuer field of a non-XAH [Currency Amount][] indicates the issuer of a token. However, when describing payments, there are special rules for the issuer field in the Amount and SendMax fields of a payment.
There is only ever one balance between two addresses for the same currency code. This means that, sometimes, the
issuerfield of an amount actually refers to a counterparty, instead of the address that issued the token.When the
issuerfield of the destinationAmountfield matches theDestinationaddress, it is treated as a special case meaning "any issuer that the destination accepts." This includes all addresses to which the destination has trust lines with a positive limit, as well as tokens with the same currency code issued by the destination.When the
issuerfield of theSendMaxfield matches the source account's address, it is treated as a special case meaning "any issuer that the source can use." This includes creating new tokens on trust lines that other accounts have extended to the source account, and sending tokens the source account holds from other issuers.
Creating Accounts
The Payment transaction type can create new accounts in Xahau by sending enough XAH to an unfunded address. Other transactions to unfunded addresses always fail.
For more information, see Accounts.
Paths
If present, the Paths field must contain a path set - an array of path arrays. Each individual path represents one way value can flow from the sender to receiver through various intermediary accounts and order books. A single transaction can potentially use multiple paths, for example if the transaction exchanges currency using several different order books to achieve the best rate.
You must omit the Paths field for direct payments, including:
An XAH-to-XAH transfer.
A direct transfer on a trust line that connects the sender and receiver.
If the Paths field is provided, the server decides at transaction processing time which paths to use, from the provided set plus a default path (the most direct way possible to connect the specified accounts). This decision is deterministic and attempts to minimize costs, but it is not guaranteed to be perfect.
The Paths field must not be an empty array, nor an array whose members are all empty arrays.
For more information, see Paths.
Payment Flags
Transactions of the Payment type support additional values in the Flags field, as follows:
tfNoDirectRipple
0x00010000
65536
Do not use the default path; only use paths included in the Paths field. This is intended to force the transaction to take arbitrage opportunities. Most clients do not need this.
tfPartialPayment
0x00020000
131072
If the specified Amount cannot be sent without spending more than SendMax, reduce the received amount instead of failing outright. See Partial Payments for more details.
tfLimitQuality
0x00040000
262144
Only take paths where all the conversions have an input:output ratio that is equal or better than the ratio of Amount:SendMax. See Limit Quality for details.
Partial Payments
A partial payment allows a payment to succeed by reducing the amount received. Partial payments are useful for returning payments without incurring additional costs to oneself. However, partial payments can also be used to exploit integrations that naively assume the Amount field of a successful transaction always describes the exact amount delivered.
A partial payment is any [Payment transaction][] with the tfPartialPayment flag enabled. A partial payment can be successful if it delivers any positive amount greater than or equal to its DeliverMin field (or any positive amount at all if DeliverMin is not specified) without sending more than the SendMax value.
The delivered_amount field of a payment's metadata indicates the amount of currency actually received by the destination account.
For more information, see the full article on Partial Payments.
Limit Quality
Xahau defines the "quality" of a currency exchange as the ratio of the numeric amount in to the numeric amount out. For example, if you spend $2 USD to receive £1 GBP, then the "quality" of that exchange is 0.5.
The tfLimitQuality flag allows you to set a minimum quality of conversions that you are willing to take. This limit quality is defined as the destination Amount divided by the SendMax amount (the numeric amounts only, regardless of currency). When set, the payment processing engine avoids using any paths whose quality (conversion rate) is worse (numerically lower) than the limit quality.
By itself, the tfLimitQuality flag reduces the number of situations in which a transaction can succeed. Specifically, it rejects payments where some part of the payment uses an unfavorable conversion, even if the overall average quality of conversions in the payment is equal or better than the limit quality. If a payment is rejected in this way, the transaction result is tecPATH_DRY.
Consider the following example. If I am trying to send you 100 Chinese Yuan (Amount = 100 CNY) for 20 United States dollars (SendMax = 20 USD) or less, then the limit quality is 5. Imagine one trader is offering ¥95 for $15 (a ratio of about 6.3 CNY per USD), but the next best offer in the market is ¥5 for $2 (a ratio of 2.5 CNY per USD). If I were to take both offers to send you 100 CNY, then it would cost me 17 USD, for an average quality of about 5.9.
Without the tfLimitQuality flag set, this transaction would succeed, because the $17 it costs me is within my specified SendMax. However, with the tfLimitQuality flag enabled, the transaction would fail instead, because the path to take the second offer has a quality of 2.5, which is worse than the limit quality of 5.
The tfLimitQuality flag is most useful when combined with partial payments. When both tfPartialPayment and tfLimitQuality are set on a transaction, then the transaction delivers as much of the destination Amount as it can, without using any conversions that are worse than the limit quality.
In the above example with a ¥95/$15 offer and a ¥5/$2 offer, the situation is different if my transaction has both tfPartialPayment and tfLimitQuality enabled. If we keep my SendMax of 20 USD and a destination Amount of 100 CNY, then the limit quality is still 5. However, because I am doing a partial payment, the transaction sends as much as it can instead of failing if the full destination amount cannot be sent. This means that my transaction consumes the ¥95/$15 offer, whose quality is about 6.3, but it rejects the ¥5/$2 offer because that offer's quality of 2.5 is worse than the quality limit of 5. In the end, my transaction only delivers ¥95 instead of the full ¥100, but it avoids wasting money on poor exchange rates.
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