fix: improve error handling and messaging in DFX Buy and OpenCryptoPay services (#2509)

* fix: improve error handling and messaging in DFX Buy and OpenCryptoPay services

* fix: adjust error handling in DFX Buy provider by updating `_getErrorMessage` function parameters and removing unused imports

lib/buy/dfx/dfx_buy_provider.dart

@@ -10,11 +10,11 @@ import 'package:cake_wallet/generated/i18n.dart';
 import 'package:cake_wallet/routes.dart';
 import 'package:cake_wallet/src/screens/connect_device/connect_device_page.dart';
 import 'package:cake_wallet/src/widgets/alert_with_one_action.dart';
-import 'package:cw_core/utils/proxy_wrapper.dart';
 import 'package:cake_wallet/utils/show_pop_up.dart';
 import 'package:cake_wallet/view_model/hardware_wallet/ledger_view_model.dart';
 import 'package:cw_core/crypto_currency.dart';
 import 'package:cw_core/utils/print_verbose.dart';
+import 'package:cw_core/utils/proxy_wrapper.dart';
 import 'package:cw_core/wallet_base.dart';
 import 'package:cw_core/wallet_type.dart';
 import 'package:flutter/material.dart';
@@ -115,7 +115,7 @@ class DFXBuyProvider extends BuyProvider {
       final message = responseBody['message'] ?? 'Service unavailable in your country';
       throw Exception(message);
     } else {
-      throw Exception('Failed to sign up. Status: ${response.statusCode} ${response.body}');
+      throw Exception('Failed to sign up. ${_getErrorMessage(response.statusCode, response.body)}');
     }
   }
 
@@ -401,4 +401,15 @@ class DFXBuyProvider extends BuyProvider {
     }
     return null;
   }
+
+  String _getErrorMessage(int statusCode, String body) {
+    final responseBody = jsonDecode(body) as Map<String, dynamic>;
+    final message = responseBody['message']?.toString() ?? '';
+
+    if (message.contains("address must match")) {
+      return "The wallet type must match the selected currency";
+    }
+
+    return message.isNotEmpty ? message : "Unknown error: ${statusCode}";
+  }
 }

lib/core/open_crypto_pay/exceptions.dart

@@ -4,8 +4,7 @@ class OpenCryptoPayException implements Exception {
   OpenCryptoPayException([this.message = '']);
 
   @override
-  String toString() =>
-      'OpenCryptoPayException${message.isNotEmpty ? ': $message' : ''}';
+  String toString() => message.isNotEmpty ? message : 'OpenCryptoPayException';
 }
 
 class OpenCryptoPayNotSupportedException extends OpenCryptoPayException {

lib/core/open_crypto_pay/open_cryptopay_service.dart

@@ -35,14 +35,12 @@ class OpenCryptoPayService {
     final response =
         await ProxyWrapper().get(clearnetUri: Uri.https(uri.authority, uri.path, queryParams));
 
+    final body = jsonDecode(response.body) as Map;
     if (response.statusCode == 200) {
-      final body = jsonDecode(response.body) as Map;
-
       if (body.keys.contains("txId")) return body["txId"] as String;
       throw OpenCryptoPayException(body.toString());
     }
-    throw OpenCryptoPayException(
-        "Unexpected status code ${response.statusCode} ${response.body}");
+    throw OpenCryptoPayException("${response.statusCode}: ${body["message"]}");
   }
 
   Future<void> cancelOpenCryptoPayRequest(OpenCryptoPayRequest request) async {