diff --git a/static/js/index.js b/static/js/index.js
index 318483b..a0b38ba 100644
--- a/static/js/index.js
+++ b/static/js/index.js
@@ -1338,20 +1338,24 @@ window.app = Vue.createApp({
       const fiatCurrency = Object.keys(fiatBalances)[0] || null
       const fiatAmount = fiatCurrency ? fiatBalances[fiatCurrency] : 0
 
+      // Use absolute values since balance is negative (liability = castle owes user)
+      const maxAmountSats = Math.abs(userBalance.balance)
+      const maxAmountFiat = Math.abs(fiatAmount)
+
       this.payUserDialog = {
         show: true,
         user_id: userBalance.user_id,
         username: userBalance.username,
-        maxAmount: userBalance.balance, // Positive sats amount castle owes
-        maxAmountFiat: fiatAmount, // EUR or other fiat amount
+        maxAmount: maxAmountSats, // Positive sats amount castle owes
+        maxAmountFiat: maxAmountFiat, // EUR or other fiat amount (positive)
         fiatCurrency: fiatCurrency,
-        amount: fiatCurrency ? fiatAmount : userBalance.balance, // Default to fiat if available
+        amount: fiatCurrency ? maxAmountFiat : maxAmountSats, // Default to fiat if available
         payment_method: 'lightning', // Default to lightning for paying
         description: '',
         reference: '',
         loading: false,
         paymentSuccess: false,
-        exchangeRate: fiatAmount > 0 ? userBalance.balance / fiatAmount : this.currentExchangeRate,
+        exchangeRate: maxAmountFiat > 0 ? maxAmountSats / maxAmountFiat : this.currentExchangeRate,
         originalCurrency: fiatCurrency || 'BTC'
       }
     },