fix: correct lnurl msat to sat min rounding

Author: piotr-iohk

Bitkit/Utilities/LnurlAmountConversion.swift

@@ -0,0 +1,18 @@
+import Foundation
+
+enum LnurlAmountConversion {
+    /// LNURL `minSendable` / `maxSendable` values are expressed in millisatoshis (msat).
+    ///
+    /// The UI and amount input operate in whole sats. When converting a minimum bound to sats we must round up:
+    /// `minSendable = 100500 msat` means the minimum payable amount is `101 sat` (not `100 sat`).
+    static func satsCeil(fromMsats msats: UInt64) -> UInt64 {
+        let quotient = msats / Env.msatsPerSat
+        let remainder = msats % Env.msatsPerSat
+        return remainder == 0 ? quotient : quotient + 1
+    }
+
+    /// Converts msats → sats by rounding down (safe for maximum bounds).
+    static func satsFloor(fromMsats msats: UInt64) -> UInt64 {
+        msats / Env.msatsPerSat
+    }
+}

Bitkit/ViewModels/AppViewModel.swift

@@ -253,8 +253,8 @@ extension AppViewModel {
         }
 
         var normalizedData = data
-        normalizedData.minSendable = max(1, normalizedData.minSendable / Env.msatsPerSat)
-        normalizedData.maxSendable = max(normalizedData.minSendable, normalizedData.maxSendable / Env.msatsPerSat)
+        normalizedData.minSendable = max(1, LnurlAmountConversion.satsCeil(fromMsats: normalizedData.minSendable))
+        normalizedData.maxSendable = max(normalizedData.minSendable, LnurlAmountConversion.satsFloor(fromMsats: normalizedData.maxSendable))
 
         // Check if user has enough lightning balance to pay the minimum amount
         let lightningBalance = lightningService.balances?.totalLightningBalanceSats ?? 0
@@ -292,8 +292,8 @@ extension AppViewModel {
         }
 
         var normalizedData = data
-        let minSats = max(1, minMsats / Env.msatsPerSat)
-        let maxSats = max(minSats, maxMsats / Env.msatsPerSat)
+        let minSats = max(1, LnurlAmountConversion.satsCeil(fromMsats: minMsats))
+        let maxSats = max(minSats, LnurlAmountConversion.satsFloor(fromMsats: maxMsats))
         normalizedData.minWithdrawable = minSats
         normalizedData.maxWithdrawable = maxSats