The \fBpay\fR RPC command attempts to find a route to the given destination, and send the funds it asks for\&. If the \fIbolt11\fR does not contain an amount, \fImsatoshi\fR is required, otherwise if it is specified it must be \fInull\fR\&. \fImsatoshi\fR is in millisatoshi precision; it can be a whole number, or a whole number with suffix \fImsat\fR or \fIsat\fR, or a three decimal point number with suffix \fIsat\fR, or an 1 to 11 decimal point number suffixed by \fIbtc\fR\&.
The \fIlabel\fR field is used to attach a label to payments, and is returned in lightning\-listpays(7) and lightning\-listpayments(7)\&. The \fIriskfactor\fR is described in detail in lightning\-getroute(7), and defaults to 10\&. The \fImaxfeepercent\fR limits the money paid in fees, and defaults to 0\&.5\&. The maxfeepercent\*(Aq is a percentage of the amount that is to be paid\&. The `exemptfee option can be used for tiny payments which would be dominated by the fee leveraged by forwarding nodes\&. Setting exemptfee allows the maxfeepercent check to be skipped on fees that are smaller than exemptfee (default: 5000 millisatoshi)\&.
The response will occur when the payment fails or succeeds\&. Once a payment has succeeded, calls to \fBpay\fR with the same \fIbolt11\fR will succeed immediately\&.
The command will keep finding routes and retrying the payment until it succeeds, or the given \fIretry_for\fR seconds passes\&. Note that the command may stop retrying while a pending payment is ongoing, which you need to monitor with \fBlistpayments\fR or \fBwaitsendpay\fR\&. \fIretry_for\fR defaults to 60 seconds and can only be an integer\&.
When using \fIlightning\-cli\fR, you may skip optional parameters by using \fInull\fR\&. Alternatively, use \fB\-k\fR option to provide parameters by name\&.
To protect user privacy, the payment algorithm performs some randomization\&.
.sp
.RS4
.ien\{\
\h'-04' 1.\h'+01'\c
.\}
.el\{\
.sp-1
.IP" 1."4.2
.\}
Route Randomization
.RE
.sp
.RS4
.ien\{\
\h'-04' 2.\h'+01'\c
.\}
.el\{\
.sp-1
.IP" 2."4.2
.\}
Value Randomization
.RE
.sp
Route randomization means the payment algorithm does not always use the lowest\-fee or shortest route\&. This prevents some highly\-connected node from learning all of the user payments by reducing their fees below the network average\&.
.sp
Value randomization means the payment algorithm will add a small random amount to the actual value paid to the destination\&. This prevents intervening nodes from identifying exactly how much is being transacted\&.
.sp
Both randomizations respect \fImaxfeepercent\fR\&. Route randomization plus the random value in value randomization will never exceed \fImaxfeepercent\fR of the payment\&. Route randomization will not take routes that would exceed \fImaxdelay\fR\&.
On success, this returns the payment \fIpreimage\fR which hashes to the \fIpayment_hash\fR to prove that the payment was successful\&. It will also return, a \fIgetroute_tries\fR and a \fIsendpay_tries\fR statistics for the number of times it internally called \fBgetroute\fR and \fBsendpay\fR\&.
On error, if the error occurred from a node other than the final destination, the route table will be updated so that getroute(7) should return an alternate route (if any)\&. An error from the final destination implies the payment should not be retried\&.
The \fIdata\fR field of errors will include statistics \fIgetroute_tries\fR and \fIsendpay_tries\fR\&. It will also contain a \fIfailures\fR field with detailed data about routing errors\&.
