Expanding on BOLT12

The discussion reveals an observation regarding the BOLT12 specification, which lacks a defined prefix for invoices. To address this gap, the proposal is to adopt the lni prefix, which, despite not being officially specified, is already in use by Core Lightning (CLN) for certain Remote Procedure Calls (RPC). This adoption is evident in CLN's implementation of the fetchinvoice and pay commands, as detailed in their documentation. The links to the respective RPC commands on CLN's documentation shed light on how lni is utilized within these contexts: lightning-fetchinvoice illustrates the command's use in fetching invoices, while lightning-pay demonstrates its application in payment processes. This insight suggests an unofficial but practical standard emerging within the community, underscoring the necessity for a more formalized approach to invoice prefixes in the BOLT12 specification.