From fa6dab9f744077b256e9571b37d1f3fc5fb73aa9 Mon Sep 17 00:00:00 2001
From: Jonathan Tzeng <jnthntzng@gmail.com>
Date: Wed, 19 Aug 2026 15:40:15 -0700
Subject: [PATCH] Show ramp crypto amounts at the asset's own decimal precision

The buy/sell amount field capped the crypto value at six decimals, which
was fine while every provider quoted at or below that. MoonPay raises its
buy-flow precision on September 1, 2026 (BTC to eight decimals, ETH and
SOL to nine), so the cap would start silently truncating the amount the
user is quoted.

Derive the cap from the selected asset's denomination instead, bounded at
nine decimals. Assets with more precision than a quote can express, such
as ETH at eighteen, would otherwise surface the rounding noise of the
float exchange rate the field divides by while a fiat amount is typed.
---
 CHANGELOG.md                              |  1 +
 src/components/scenes/RampCreateScene.tsx | 24 ++++++++++++++++++++++-
 2 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index e3e95a323cb..656c97fba4d 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -18,6 +18,7 @@
 - changed: (ARRR) Pirate Chain wallets run on `react-native-pirate-wallet` 0.3.4, replacing `react-native-piratechain`
 - changed: Balance-effect checks and the login FIO refresh wait for engine readiness on cache-emitted wallets
 - changed: Opening any wallet-scoped scene asks the core to prioritize that wallet's engine startup in the post-login queue.
+- changed: Buy/sell crypto amount field shows up to nine decimals, matching the asset's precision, instead of six
 - fixed: A send whose funds are not spendable yet says so instead of reporting a network error
 - fixed: Auto-login starting two competing accounts when both `YOLO_PASSWORD` and `YOLO_PIN` are set, and attempting a login when either is set to an empty string.
 - fixed: Auto-login never running on a device with no accounts, since the welcome carousel took priority over the login scene that owns it.
diff --git a/src/components/scenes/RampCreateScene.tsx b/src/components/scenes/RampCreateScene.tsx
index 2a9595fc2b0..59586cbbbe1 100644
--- a/src/components/scenes/RampCreateScene.tsx
+++ b/src/components/scenes/RampCreateScene.tsx
@@ -87,6 +87,13 @@ import { EdgeText } from '../themed/EdgeText'
 import { FilledTextInput } from '../themed/FilledTextInput'
 import { RampRegionSelect } from './RampCreateScene/RampRegionSelect'
 
+/**
+ * Upper bound on the decimals the crypto amount field renders, for assets whose
+ * own precision goes beyond what a ramp quote can express. See
+ * `cryptoMaxDecimals`.
+ */
+const MAX_CRYPTO_ENTRY_DECIMALS = 9
+
 export interface RampCreateParams {
   forcedWalletResult?: WalletListWalletResult
   regionCode?: string
@@ -617,6 +624,21 @@ export const RampCreateScene: React.FC<Props> = (props: Props) => {
     denomination
   ])
 
+  // How many decimals the crypto field renders. Providers quote each asset at
+  // its own precision and change it over time (Moonpay moves BTC 5 -> 8 and
+  // ETH/SOL to 9 decimals on the buy flow in September 2026), so this follows
+  // the asset instead of assuming a count. The 9-decimal ceiling keeps the
+  // field readable for high-precision assets such as ETH, whose 18 decimals
+  // would expose the rounding noise of the float exchange rate that
+  // `displayCryptoAmount` divides by while the user types a fiat amount.
+  const cryptoMaxDecimals = React.useMemo(() => {
+    if (denomination == null) return MAX_CRYPTO_ENTRY_DECIMALS
+    return Math.min(
+      mulToPrecision(denomination.multiplier),
+      MAX_CRYPTO_ENTRY_DECIMALS
+    )
+  }, [denomination])
+
   // Log the quote event only when the scene is focused
   useFocusEffect(() => {
     dispatch(logEvent(direction === 'buy' ? 'Buy_Quote' : 'Sell_Quote'))
@@ -1129,7 +1151,7 @@ export const RampCreateScene: React.FC<Props> = (props: Props) => {
                 placeholder={cryptoAmountPlaceholder}
                 keyboardType="decimal-pad"
                 numeric
-                maxDecimals={6}
+                maxDecimals={cryptoMaxDecimals}
                 returnKeyType="done"
                 showSpinner={isFetchingQuotes && lastUsedInput === 'fiat'}
                 disabled={cryptoInputDisabled}