diff --git a/05.md b/05.md
index 651d2422..e21b6e53 100644
--- a/05.md
+++ b/05.md
@@ -28,10 +28,15 @@ The wallet `Alice` includes the following `PostMeltQuoteBolt11Request` data in i
 {
   "request": <str>,
   "unit": <str_enum[UNIT]>
+  "options": { // Optional
+    "amountless": {
+      "amount_msat": <int>
+    }
+  }
 }
 ```
 
-Here, `request` is the bolt11 Lightning invoice to be paid and `unit` is the unit the wallet would like to pay with.
+Here, `request` is the bolt11 Lightning invoice to be paid and `unit` is the unit the wallet would like to pay with. `amount` **MAY** be passed to pay amountless bolt11 invoices. The `amount` **MUST** be in msat and if the bolt11 invoice has an amount, the `amount` field **MUST** be equal to the amount of the bolt11 invoice. The request **MAY** be an amountless invoice only if support for amountless invoices is signaled in the `MeltMethodSettings`.
 
 The mint `Bob` then responds with a `PostMeltQuoteBolt11Response`:
 
@@ -188,11 +193,12 @@ The mint's settings for this nut indicate the supported method-unit pairs for me
   "method": <str>,
   "unit": <str>,
   "min_amount": <int|null>,
-  "max_amount": <int|null>
+  "max_amount": <int|null>,
+  "amountless": <bool|null>
 }
 ```
 
-`min_amount` and `max_amount` indicate the minimum and maximum amount for an operation of this method-unit pair.
+`min_amount` and `max_amount` indicate the minimum and maximum amount for an operation of this method-unit pair. `amountless` signals if the backed supports paying an amountless invoice.
 
 Example `MeltMethodSetting`:
 
@@ -201,7 +207,8 @@ Example `MeltMethodSetting`:
   "method": "bolt11",
   "unit": "sat",
   "min_amount": 100,
-  "max_amount": 10000
+  "max_amount": 10000,
+  "amountless": true
 }
 ```
 
diff --git a/error_codes.md b/error_codes.md
index bd758a9f..8ef94754 100644
--- a/error_codes.md
+++ b/error_codes.md
@@ -12,6 +12,8 @@
 | 11008 | Duplicate outputs provided                      | [NUT-03][03], [NUT-04][04], [NUT-05][05] |
 | 11009 | Inputs/Outputs of multiple units                | [NUT-03][03], [NUT-04][04], [NUT-05][05] |
 | 11010 | Inputs and outputs not of same unit             | [NUT-03][03], [NUT-04][04], [NUT-05][05] |
+| 11011 | Amountless invoice is not supported             | [NUT-05][05]                             |
+| 11012 | Amount in request does not equal invoice        | [NUT-05][05]                             |
 | 12001 | Keyset is not known                             | [NUT-02][02], [NUT-04][04]               |
 | 12002 | Keyset is inactive, cannot sign messages        | [NUT-02][02], [NUT-03][03], [NUT-04][04] |
 | 20001 | Quote request is not paid                       | [NUT-04][04]                             |