Add error handling

src/Umbraco.Commerce.PaymentProviders.Nets/Easy/Api/Models/NetsErrorResponse.cs

@@ -0,0 +1,11 @@
+using System.Collections.Generic;
+using System.Text.Json.Serialization;
+
+namespace Umbraco.Commerce.PaymentProviders.Api.Models
+{
+    public class NetsErrorResponse
+    {
+        [JsonPropertyName("errors")]
+        public Dictionary<string, List<string>> Errors { get; set; }
+    }
+}

src/Umbraco.Commerce.PaymentProviders.Nets/Easy/Api/Models/NetsServerErrorResponse.cs

@@ -0,0 +1,17 @@
+using System.Collections.Generic;
+using System.Text.Json.Serialization;
+
+namespace Umbraco.Commerce.PaymentProviders.Api.Models
+{
+    public class NetsServerErrorResponse
+    {
+        [JsonPropertyName("message")]
+        public string Message { get; set; }
+
+        [JsonPropertyName("code")]
+        public string Code { get; set; }
+
+        [JsonPropertyName("source")]
+        public string Source { get; set; }
+    }
+}

src/Umbraco.Commerce.PaymentProviders.Nets/Easy/Api/NetsApiException.cs

@@ -0,0 +1,58 @@
+using System;
+using System.Linq;
+using System.Net;
+using Umbraco.Commerce.PaymentProviders.Api.Models;
+
+namespace Umbraco.Commerce.PaymentProviders.Api
+{
+    public class NetsApiException : Exception
+    {
+        public HttpStatusCode StatusCode { get; }
+        public NetsErrorResponse ValidationErrors { get; }
+        public NetsServerErrorResponse ServerError { get; }
+
+        public NetsApiException() { }
+
+        public NetsApiException(string message) : base(message) { }
+
+        public NetsApiException(string message, Exception innerException) : base(message, innerException) { }
+
+        public NetsApiException(HttpStatusCode statusCode, NetsErrorResponse validationErrors)
+         : base(FormatValidationErrorMessage(validationErrors))
+        {
+            StatusCode = statusCode;
+            ValidationErrors = validationErrors;
+        }
+
+        public NetsApiException(HttpStatusCode statusCode, NetsServerErrorResponse serverError)
+        : base(FormatServerErrorMessage(serverError))
+        {
+            StatusCode = statusCode;
+            ServerError = serverError;
+        }
+
+        private static string FormatValidationErrorMessage(NetsErrorResponse errorResponse)
+        {
+            if (errorResponse?.Errors == null || errorResponse.Errors.Count == 0)
+            {
+                return "Validation failed, but no error details were provided.";
+            }
+
+            var errors = string.Join(" ", errorResponse.Errors
+                   .Where(e => e.Value is { Count: >0 })
+                   .Select(e => $"{e.Key}: {string.Join(", ", e.Value)}"));
+
+            return $"Validation Errors: {errors}";
+        }
+
+        private static string FormatServerErrorMessage(NetsServerErrorResponse serverError)
+        {
+            if (serverError == null)
+            {
+                return "An unknown internal server error occurred.";
+            }
+
+            return $"Internal Server Error: {serverError.Message} (Code: {serverError.Code}, Source: {serverError.Source})";
+        }
+    }
+}

src/Umbraco.Commerce.PaymentProviders.Nets/Easy/Api/NetsEasyClient.cs

@@ -1,4 +1,6 @@
 using System;
+using System.Collections.Generic;
+using System.Net;
 using System.Text.Json.Serialization;
 using System.Threading;
 using System.Threading.Tasks;
@@ -62,8 +64,6 @@ public async Task<NetsRefund> RefundPaymentAsync(string chargeId, object data, C
 
         private async Task<TResult> RequestAsync<TResult>(string url, Func<IFlurlRequest, CancellationToken, Task<TResult>> func, CancellationToken cancellationToken = default)
         {
-            var result = default(TResult);
-
             try
             {
                 var req = new FlurlRequest(_config.BaseUrl + url)
@@ -78,14 +78,61 @@ private async Task<TResult> RequestAsync<TResult>(string url, Func<IFlurlRequest
                         })
                         .WithHeader("Authorization", _config.Authorization);
 
-                result = await func.Invoke(req, cancellationToken).ConfigureAwait(false);
+                return await func.Invoke(req, cancellationToken).ConfigureAwait(false);
             }
             catch (FlurlHttpException ex)
             {
-                throw;
-            }
+                HttpStatusCode statusCode = ex.StatusCode.HasValue ? (HttpStatusCode)ex.StatusCode.Value : HttpStatusCode.BadRequest;
+
+                if (statusCode == HttpStatusCode.Unauthorized)
+                {
+                    throw new NetsApiException(HttpStatusCode.Unauthorized, new NetsErrorResponse
+                    {
+                        Errors = new Dictionary<string, List<string>> { { "Authorization", new List<string> { "Unauthorized request - Missing or invalid secret." } } }
+                    });
+                }
+
+                if (statusCode == HttpStatusCode.InternalServerError)
+                {
+                    NetsServerErrorResponse netsServerErrorResponse = null;
+                    try
+                    {
+                        netsServerErrorResponse = await ex.GetResponseJsonAsync<NetsServerErrorResponse>().ConfigureAwait(false);
+                    }
+                    catch
+                    {
+                        netsServerErrorResponse = new NetsServerErrorResponse
+                        {
+                            Message = "An unexpected internal server error occurred.",
+                            Code = "Unknown",
+                            Source = "Unknown"
+                        };
+                    }
 
-            return result;
+                    throw new NetsApiException(statusCode, netsServerErrorResponse);
+                }
+
+                if (statusCode == HttpStatusCode.BadRequest)
+                {
+                    NetsErrorResponse netsErrorResponse = null;
+                    try
+                    {
+                        netsErrorResponse = await ex.GetResponseJsonAsync<NetsErrorResponse>().ConfigureAwait(false);
+                    }
+                    catch
+                    {
+                        netsErrorResponse = new NetsErrorResponse
+                        {
+                            Errors = new Dictionary<string, List<string>> { { "UnknownError", new List<string> { "A validation error occurred, but details could not be retrieved." } } }
+                        };
+                    }
+
+                    throw new NetsApiException(statusCode, netsErrorResponse);
+                }
+
+                string rawResponse = await ex.GetResponseStringAsync().ConfigureAwait(false);
+                throw new NetsApiException($"Unexpected error from Nets API (Status {statusCode}): {rawResponse}");
+            }
         }
     }
 }