diff --git a/frontend/src/components/admin/user/UserBalanceModal.vue b/frontend/src/components/admin/user/UserBalanceModal.vue
index e8474cff02..f0070b0340 100644
--- a/frontend/src/components/admin/user/UserBalanceModal.vue
+++ b/frontend/src/components/admin/user/UserBalanceModal.vue
@@ -29,6 +29,7 @@ import { reactive, ref, watch } from 'vue'
 import { useI18n } from 'vue-i18n'
 import { useAppStore } from '@/stores/app'
 import { adminAPI } from '@/api/admin'
+import { extractApiErrorMessage } from '@/utils/apiError'
 import type { AdminUser } from '@/types'
 import BaseDialog from '@/components/common/BaseDialog.vue'
 
@@ -80,7 +81,7 @@ const handleBalanceSubmit = async () => {
     appStore.showSuccess(t('common.success')); emit('success'); emit('close')
   } catch (e: any) {
     console.error('Failed to update balance:', e)
-    appStore.showError(e.response?.data?.detail || t('common.error'))
+    appStore.showError(extractApiErrorMessage(e, t('common.error')))
   } finally { submitting.value = false }
 }
 </script>
diff --git a/frontend/src/components/admin/user/__tests__/UserBalanceModal.spec.ts b/frontend/src/components/admin/user/__tests__/UserBalanceModal.spec.ts
new file mode 100644
index 0000000000..068bc2424d
--- /dev/null
+++ b/frontend/src/components/admin/user/__tests__/UserBalanceModal.spec.ts
@@ -0,0 +1,27 @@
+import { enableAutoUnmount, flushPromises, mount } from '@vue/test-utils'
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest'
+import UserBalanceModal from '../UserBalanceModal.vue'
+import type { AdminUser } from '@/types'
+const mocks = vi.hoisted(() => ({ updateBalance: vi.fn(), showError: vi.fn(), showSuccess: vi.fn() }))
+vi.mock('@/api/admin', () => ({ adminAPI: { users: mocks } }))
+vi.mock('@/stores/app', () => ({ useAppStore: () => mocks }))
+vi.mock('vue-i18n', () => ({ useI18n: () => ({ t: (key: string) => key }) }))
+enableAutoUnmount(afterEach)
+beforeEach(() => { vi.clearAllMocks(); vi.spyOn(console, 'error').mockImplementation(() => {}) })
+afterEach(() => vi.restoreAllMocks())
+describe('balance operation error feedback', () => {
+  it.each([
+    [{ message: 'User balance changed; retry' }, 'User balance changed; retry'],
+    [{ response: { data: { detail: 'Legacy detail' } } }, 'Legacy detail'],
+    [{}, 'common.error'],
+  ])('shows the available API error and keeps the dialog open', async (error, message) => {
+    mocks.updateBalance.mockRejectedValueOnce(error)
+    const w = mount(UserBalanceModal, { props: { show: true, operation: 'add', user: { id: 1, email: 'a@example.com', balance: 5 } as AdminUser },
+      global: { stubs: { BaseDialog: { template: '<div><slot /><slot name="footer" /></div>' } } } })
+    await w.get('input[type="number"]').setValue('1')
+    await w.get('form').trigger('submit'); await flushPromises()
+    expect(mocks.showError).toHaveBeenCalledWith(message)
+    expect(w.emitted('success')).toBeUndefined(); expect(w.emitted('close')).toBeUndefined()
+    expect(w.get('button[type="submit"]').attributes('disabled')).toBeUndefined()
+  })
+})