Function interledger::spsp::pay

pub fn pay<S, A>(
    service: S, 
    from_account: A, 
    receiver: &str, 
    source_amount: u64
) -> impl Future<Item = u64, Error = Error> where
    A: Account,
    S: IncomingService<A> + Clone, 

Query the details of the given Payment Pointer and send a payment using the STREAM protocol.

This returns the amount delivered, as reported by the receiver and in the receiver's asset's units.