NUT-XX: Multinut payments

08.md

@@ -1,7 +1,7 @@
 NUT-08: Lightning fee return
 ==========================
 
-`optional`
+`optional`, `depends on: NUT-05`
 
 ---
 

11.md

@@ -1,7 +1,7 @@
 NUT-11: Pay to Public Key (P2PK)
 ==========================
 
-`optional`
+`optional`, `depends on: NUT-10`
 
 ---
 

14.md

@@ -0,0 +1,61 @@
+NUT-14: Partial multi-path payments
+==========================
+
+`optional` `depends on: NUT-05`
+
+---
+
+In this document, we describe how wallets can instruct multiple mints to each pay a partial amount of a bolt11 Lightning invoice. The full payment is composed of partial payments (MPP) from multiple multi-path payments from different Lightning nodes. This way, wallets can pay a larger Lightning invoice combined from multiple smaller balances on different mints. Due to the atomic nature of MPP, either all payments wil be successful or all of them will fail.
+
+The Lightning backend of the mint must support paying a partial amount of an Invoice and multi-path payments (MPP, see [BOLT 4](https://github.com/lightning/bolts/blob/master/04-onion-routing.md)). For example, the mint's Lightning node must be able to pay 50 sats of a 100 sat bolt11 invoice. The receiving Lightning node must support receiving multi-path payments as well.
+
+# Multimint payment execution
+
+`Alice`'s wallet coordinates multiple MPPs on different mints that support the feature (see below for the indicated settings). For a given Lightning invoice of `amount_total`, `Alice` splits the total amount into several partial amounts `amount_total = amount_1 + amount_2 + ...` that each must be covered by her individual balances on the mints she wants to use for the payment. Then she constructs multiple `PostMeltQuoteBolt11Request`'s that each include the corresponding partial amount (see below) that she sends to all mints she wants to use for the payment. The mints then respond with a normal `PostMeltQuoteBolt11Response` (see [NUT-05][05]). `Alice` proceeds to pay the melt requests at each mint simultaneously. When all mints have sent out the Lightning payment, she receives a successful response from all mints individually.
+
+# Melt quote
+
+To request a melt quote with a partial `amount`, the wallet of `Alice` makes a `POST /v1/melt/quote/{method}` request where `method` is the payment method requested (here `bolt11`). 
+
+```http
+POST https://mint.host:3338/v1/melt/quote/bolt11
+```
+
+The wallet `Alice` includes the following `PostMeltQuoteBolt11Request` data in its request which includes an additional `amount` field compared to the standard request in [NUT-05][05]:
+
+```json
+{
+  "request": <str>,
+  "unit": <str_enum["sat"]>,
+  "amount": <int> # <-- new
+}
+```
+
+Here, `request` is the bolt11 Lightning invoice to be paid, `unit` is the unit the wallet would like to pay with, and `amount` is the amount for the requested payment. The wallet then pays the returned melt quote the same way as in [NUT-05][05].
+
+## Settings
+
+The settings indicating that a mint supports this feature are in the `MeltMethodSetting` (see [NUT-05][05]) which is returned in the info endpoint ([NUT-06][06]). The mint MUST indicate `method` and `unit` pairs that support `mpp`.
+
+`MeltMethodSetting` is of the form:
+```json
+{
+  ...,
+  "mpp": <bool>
+}
+```
+
+Example `MeltMethodSetting`:
+
+```json
+{
+  "method": "bolt11",
+  "unit": "sat",
+  "min_amount": 100,
+  "max_amount": 10000,
+  "mpp": true     
+}
+```
+
+[05]: 05.md
+[06]: 06.md