Add message to clarify import JSON v5

lib/ui/settings/import_export.dart

@@ -10,6 +10,7 @@ import 'package:file_picker/file_picker.dart';
 import 'package:flutter_redux/flutter_redux.dart';
 import 'package:flutter_styled_toast/flutter_styled_toast.dart';
 import 'package:http/http.dart';
+import 'package:invoiceninja_flutter/ui/app/help_text.dart';
 import 'package:material_design_icons_flutter/material_design_icons_flutter.dart';
 
 // Project imports:
@@ -331,6 +332,13 @@ class _FileImportState extends State<_FileImport> {
 
     if (widget.importType == ImportType.json) {
       children.addAll([
+        Padding(
+          padding: const EdgeInsets.only(bottom: 8),
+          child: Text(
+            localization.jsonHelp,
+            style: TextStyle(color: Colors.grey),
+          ),
+        ),
         SwitchListTile(
           activeColor: Theme.of(context).colorScheme.secondary,
           title: Text(localization.importSettings),

lib/utils/i18n.dart

@@ -16,6 +16,7 @@ mixin LocalizationsProvider on LocaleCodeAware {
   static final Map<String, Map<String, String>> _localizedValues = {
     'en': {
       // STARTER: lang key - do not remove comment
+      'json_help': 'Note: JSON files generated by the v4 app are not supported',
       'release_notes': 'Release Notes',
       'upgrade_to_view_reports': 'Upgrade your plan to view reports',
       'started_tasks': 'Successfully started :value tasks',
@@ -74170,6 +74171,10 @@ mixin LocalizationsProvider on LocaleCodeAware {
       _localizedValues[localeCode]['release_notes'] ??
       _localizedValues['en']['release_notes'];
 
+  String get jsonHelp =>
+      _localizedValues[localeCode]['json_help'] ??
+      _localizedValues['en']['json_help'];
+
   // STARTER: lang field - do not remove comment
 
   String lookup(String key) {