The SubscribeInvoices endpoint provides a stream of updates for lnd’s invoices, informing you about newly added invoices and sending notifications when they are settled. This endpoint supports historical streams, and can be queried with an add_index to query all invoices that were added after the index provided, or a settle_invoice to query all invoices that were settled after the invoice provided. This can be helpful for syncing up your program’s state after a restart. If you would like to subscribe to individual invoices, SubscribeSingleInvoice can be queried with the invoice’s payment hash as an identifier.