in src/main/scala/com/gu/invoicing/invoice/Impl.scala [160:167]
def tagMultiSubInvoices(invoices: List[MmaInvoiceWithPayment]): List[MmaInvoiceWithPayment] = {
invoices
.groupBy(_.invoiceId)
.flatMap { case (id, invoices) =>
invoices.map(_.copy(hasMultipleSubs = invoices.length > 1))
}
.toList
}