diff --git a/src/RobinTTY.NordigenApiClient.Tests/LiveApi/CredentialTests.cs b/src/RobinTTY.NordigenApiClient.Tests/LiveApi/CredentialTests.cs
index a5dd405..d8cbdd0 100644
--- a/src/RobinTTY.NordigenApiClient.Tests/LiveApi/CredentialTests.cs
+++ b/src/RobinTTY.NordigenApiClient.Tests/LiveApi/CredentialTests.cs
@@ -2,6 +2,7 @@
 using RobinTTY.NordigenApiClient.Models;
 using RobinTTY.NordigenApiClient.Models.Requests;
 using RobinTTY.NordigenApiClient.Models.Responses;
+using RobinTTY.NordigenApiClient.Tests.Shared;
 
 namespace RobinTTY.NordigenApiClient.Tests.LiveApi;
 
@@ -29,7 +30,7 @@ public async Task MakeRequestWithInvalidCredentials()
         Assert.Multiple(() =>
         {
             Assert.That(agreementsResponse.StatusCode, Is.EqualTo(HttpStatusCode.Unauthorized));
-            Assert.That(ErrorMatchesExpectation(agreementsResponse.Error!), Is.True);
+            AssertErrorMatchesExpectation(agreementsResponse.Error!);
         });
 
         // Returns InstitutionsError
@@ -37,7 +38,7 @@ public async Task MakeRequestWithInvalidCredentials()
         Assert.Multiple(() =>
         {
             Assert.That(institutionResponse.StatusCode, Is.EqualTo(HttpStatusCode.Unauthorized));
-            Assert.That(ErrorMatchesExpectation(institutionResponse.Error!), Is.True);
+            AssertErrorMatchesExpectation(institutionResponse.Error!);
         });
 
         // Returns AccountsError
@@ -45,7 +46,7 @@ public async Task MakeRequestWithInvalidCredentials()
         Assert.Multiple(() =>
         {
             Assert.That(balancesResponse.StatusCode, Is.EqualTo(HttpStatusCode.Unauthorized));
-            Assert.That(ErrorMatchesExpectation(balancesResponse.Error!), Is.True);
+            AssertErrorMatchesExpectation(balancesResponse.Error!);
             Assert.That(
                 new object?[]
                 {
@@ -61,7 +62,7 @@ public async Task MakeRequestWithInvalidCredentials()
         Assert.Multiple(() =>
         {
             Assert.That(balancesResponse.StatusCode, Is.EqualTo(HttpStatusCode.Unauthorized));
-            Assert.That(ErrorMatchesExpectation(createAgreementResponse.Error!), Is.True);
+            AssertErrorMatchesExpectation(createAgreementResponse.Error!);
             Assert.That(new object?[]
             {
                 createAgreementResponse.Error!.AccessScopeError, createAgreementResponse.Error.AccessValidForDaysError,
@@ -78,7 +79,7 @@ public async Task MakeRequestWithInvalidCredentials()
         Assert.Multiple(() =>
         {
             Assert.That(balancesResponse.StatusCode, Is.EqualTo(HttpStatusCode.Unauthorized));
-            Assert.That(ErrorMatchesExpectation(requisitionResponse.Error!), Is.True);
+            AssertErrorMatchesExpectation(requisitionResponse.Error!);
             Assert.That(new object?[]
             {
                 requisitionResponse.Error!.AgreementError, requisitionResponse.Error.InstitutionIdError,
@@ -89,8 +90,7 @@ public async Task MakeRequestWithInvalidCredentials()
         });
     }
 
-    private static bool ErrorMatchesExpectation(BasicResponse error)
-    {
-        return error is {Detail: "Authentication credentials were not provided.", Summary: "Authentication failed"};
-    }
+    private static void AssertErrorMatchesExpectation(BasicResponse error) =>
+        AssertionHelpers.AssertBasicResponseMatchesExpectations(error, "Authentication failed",
+            "No active account found with the given credentials");
 }
diff --git a/src/RobinTTY.NordigenApiClient/Models/Errors/AccountsError.cs b/src/RobinTTY.NordigenApiClient/Models/Errors/AccountsError.cs
index e016350..71f5be1 100644
--- a/src/RobinTTY.NordigenApiClient/Models/Errors/AccountsError.cs
+++ b/src/RobinTTY.NordigenApiClient/Models/Errors/AccountsError.cs
@@ -31,6 +31,7 @@ public class AccountsError : BasicResponse
 #endif
     [JsonPropertyName("date_from")]
     public BasicResponse? StartDateError { get; }
+
 #if NET6_0_OR_GREATER
     /// <summary>
     /// An error that was returned related to the
@@ -48,6 +49,12 @@ public class AccountsError : BasicResponse
 #endif
     [JsonPropertyName("date_to")]
     public BasicResponse? EndDateError { get; }
+    
+    /// <summary>
+    /// Creates a new instance of <see cref="AccountsError" />.
+    /// </summary>
+    public AccountsError(){}
+
 #if NET6_0_OR_GREATER
     /// <summary>
     /// Creates a new instance of <see cref="AccountsError" />.
diff --git a/src/RobinTTY.NordigenApiClient/Models/Errors/CreateAgreementError.cs b/src/RobinTTY.NordigenApiClient/Models/Errors/CreateAgreementError.cs
index abbe5a7..4ae401b 100644
--- a/src/RobinTTY.NordigenApiClient/Models/Errors/CreateAgreementError.cs
+++ b/src/RobinTTY.NordigenApiClient/Models/Errors/CreateAgreementError.cs
@@ -43,6 +43,11 @@ public class CreateAgreementError : BasicResponse
     /// </summary>
     [JsonPropertyName("agreement")]
     public BasicResponse? AgreementError { get; }
+    
+    /// <summary>
+    /// Creates a new instance of <see cref="CreateAgreementError" />.
+    /// </summary>
+    public CreateAgreementError(){}
 
     /// <summary>
     /// Creates a new instance of <see cref="CreateAgreementError" />.
diff --git a/src/RobinTTY.NordigenApiClient/Models/Errors/CreateRequisitionError.cs b/src/RobinTTY.NordigenApiClient/Models/Errors/CreateRequisitionError.cs
index 14c3ae2..07a8885 100644
--- a/src/RobinTTY.NordigenApiClient/Models/Errors/CreateRequisitionError.cs
+++ b/src/RobinTTY.NordigenApiClient/Models/Errors/CreateRequisitionError.cs
@@ -57,6 +57,11 @@ public class CreateRequisitionError : BasicResponse
     /// </summary>
     [JsonPropertyName("institution_id")]
     public BasicResponse? InstitutionIdError { get; }
+    
+    /// <summary>
+    /// Creates a new instance of <see cref="CreateRequisitionError" />.
+    /// </summary>
+    public CreateRequisitionError(){}
 
     /// <summary>
     /// Creates a new instance of <see cref="CreateRequisitionError" />.
diff --git a/src/RobinTTY.NordigenApiClient/Models/Errors/InstitutionsError.cs b/src/RobinTTY.NordigenApiClient/Models/Errors/InstitutionsError.cs
index f9201b0..09684ac 100644
--- a/src/RobinTTY.NordigenApiClient/Models/Errors/InstitutionsError.cs
+++ b/src/RobinTTY.NordigenApiClient/Models/Errors/InstitutionsError.cs
@@ -8,6 +8,11 @@ namespace RobinTTY.NordigenApiClient.Models.Errors;
 /// </summary>
 public class InstitutionsError : BasicResponse
 {
+    /// <summary>
+    /// Creates a new instance of <see cref="InstitutionsError" />.
+    /// </summary>
+    public InstitutionsError(){}
+    
     /// <summary>
     /// Creates a new instance of <see cref="InstitutionsError" />.
     /// </summary>
@@ -23,19 +28,12 @@ public InstitutionsError(BasicResponse country) : base(country.Summary, country.
 /// Since this representation doesn't add any useful information (only extra encapsulation)
 /// it is transformed to align this error with other errors returned by the API.
 /// </summary>
-internal class InstitutionsErrorInternal
+[method: JsonConstructor]
+internal class InstitutionsErrorInternal(BasicResponse? country, string? summary, string? detail)
 {
-    [JsonPropertyName("country")] public BasicResponse? Country { get; }
-
-    [JsonPropertyName("summary")] public string? Summary { get; }
+    [JsonPropertyName("country")] public BasicResponse? Country { get; } = country;
 
-    [JsonPropertyName("detail")] public string? Detail { get; }
+    [JsonPropertyName("summary")] public string? Summary { get; } = summary;
 
-    [JsonConstructor]
-    public InstitutionsErrorInternal(BasicResponse? country, string? summary, string? detail)
-    {
-        Country = country;
-        Summary = summary;
-        Detail = detail;
-    }
+    [JsonPropertyName("detail")] public string? Detail { get; } = detail;
 }
diff --git a/src/RobinTTY.NordigenApiClient/Models/Responses/BasicResponse.cs b/src/RobinTTY.NordigenApiClient/Models/Responses/BasicResponse.cs
index 314f86a..d192839 100644
--- a/src/RobinTTY.NordigenApiClient/Models/Responses/BasicResponse.cs
+++ b/src/RobinTTY.NordigenApiClient/Models/Responses/BasicResponse.cs
@@ -11,14 +11,19 @@ public class BasicResponse
     /// The summary text of the response/error.
     /// </summary>
     [JsonPropertyName("summary")]
-    public string? Summary { get; }
+    public string? Summary { get; init; }
 
     /// <summary>
     /// The detailed description of the response/error.
     /// </summary>
     [JsonPropertyName("detail")]
-    public string? Detail { get; }
-
+    public string? Detail { get; init; }
+    
+    /// <summary>
+    /// Creates a new instance of <see cref="BasicResponse" />.
+    /// </summary>
+    public BasicResponse(){}
+    
     /// <summary>
     /// Creates a new instance of <see cref="BasicResponse" />.
     /// </summary>
diff --git a/src/RobinTTY.NordigenApiClient/Models/Responses/ResponsePage.cs b/src/RobinTTY.NordigenApiClient/Models/Responses/ResponsePage.cs
index 6038a92..4b3c80c 100644
--- a/src/RobinTTY.NordigenApiClient/Models/Responses/ResponsePage.cs
+++ b/src/RobinTTY.NordigenApiClient/Models/Responses/ResponsePage.cs
@@ -1,5 +1,4 @@
 using System.Text.Json.Serialization;
-using RobinTTY.NordigenApiClient.Models.Errors;
 
 namespace RobinTTY.NordigenApiClient.Models.Responses;
 
diff --git a/src/RobinTTY.NordigenApiClient/NordigenClient.cs b/src/RobinTTY.NordigenApiClient/NordigenClient.cs
index 54cd3aa..ec93b7c 100644
--- a/src/RobinTTY.NordigenApiClient/NordigenClient.cs
+++ b/src/RobinTTY.NordigenApiClient/NordigenClient.cs
@@ -1,4 +1,5 @@
-using System.Text.Json;
+using System.Net;
+using System.Text.Json;
 using RobinTTY.NordigenApiClient.Contracts;
 using RobinTTY.NordigenApiClient.Endpoints;
 using RobinTTY.NordigenApiClient.JsonConverters;
@@ -34,7 +35,7 @@ public class NordigenClient : INordigenClient
 
     /// <inheritdoc />
     public IAccountsEndpoint AccountsEndpoint { get; }
-    
+
     /// <inheritdoc />
     public event EventHandler<TokenPairUpdatedEventArgs>? TokenPairUpdated;
 
@@ -69,6 +70,18 @@ public NordigenClient(HttpClient httpClient, NordigenClientCredentials credentia
         AccountsEndpoint = new AccountsEndpoint(this);
     }
 
+    /// <summary>
+    /// Carries out the request to the GoCardless API, gathering a valid JWT if necessary.
+    /// </summary>
+    /// <param name="uri">The URI of the API endpoint.</param>
+    /// <param name="method">The <see cref="HttpMethod"/> to use for this request.</param>
+    /// <param name="cancellationToken">Token to signal cancellation of the operation.</param>
+    /// <param name="query">Optional query parameters to add to the request.</param>
+    /// <param name="body">Optional body to add to the request.</param>
+    /// <param name="useAuthentication">Whether to use authentication.</param>
+    /// <typeparam name="TResponse">The type of the response.</typeparam> 
+    /// <typeparam name="TError">The type of the error.</typeparam>
+    /// <returns>The response to the request.</returns>
     internal async Task<NordigenApiResponse<TResponse, TError>> MakeRequest<TResponse, TError>(
         string uri,
         HttpMethod method,
@@ -76,16 +89,29 @@ internal async Task<NordigenApiResponse<TResponse, TError>> MakeRequest<TRespons
         IEnumerable<KeyValuePair<string, string>>? query = null,
         HttpContent? body = null,
         bool useAuthentication = true
-    ) where TResponse : class where TError : class
+    ) where TResponse : class where TError : BasicResponse, new()
     {
         var requestUri = query != null ? uri + UriQueryBuilder.GetQueryString(query) : uri;
         HttpClient client;
+
+        // When an endpoint that requires authentication is called the client tries to update the JWT first
+        // - The updating is done using a semaphore to avoid multiple threads trying to update the token simultaneously
+        // - If the request to get the token succeeds, the subsequent request is executed
+        // - If the request to get the token fails, the error response from the token endpoint is returned instead
         if (useAuthentication)
         {
             await TokenSemaphore.WaitAsync(cancellationToken);
+
             try
             {
-                JsonWebTokenPair = await TryGetValidTokenPair(cancellationToken);
+                var tokenResponse = await TryGetValidTokenPair(cancellationToken);
+
+
+                if (tokenResponse.IsSuccess)
+                    JsonWebTokenPair = tokenResponse.Result;
+                else
+                    return new NordigenApiResponse<TResponse, TError>(tokenResponse.StatusCode, tokenResponse.IsSuccess,
+                        null, new TError {Summary = tokenResponse.Error.Summary, Detail = tokenResponse.Error.Detail});
             }
             finally
             {
@@ -99,38 +125,47 @@ internal async Task<NordigenApiResponse<TResponse, TError>> MakeRequest<TRespons
             client = _httpClient;
         }
 
-        HttpResponseMessage? response;
-        if (method == HttpMethod.Get)
-            response = await client.GetAsync(requestUri, cancellationToken);
-        else if (method == HttpMethod.Post)
-            response = await client.PostAsync(requestUri, body, cancellationToken);
-        else if (method == HttpMethod.Delete)
-            response = await client.DeleteAsync(requestUri, cancellationToken);
-        else if (method == HttpMethod.Put)
-            response = await client.PutAsync(requestUri, body, cancellationToken);
-        else
-            throw new NotImplementedException();
+        var response = await ExecuteRequest(client, method, requestUri, cancellationToken, body);
 
         return await NordigenApiResponse<TResponse, TError>.FromHttpResponse(response, _serializerOptions,
             cancellationToken);
     }
 
+    private static async Task<HttpResponseMessage> ExecuteRequest(HttpClient client, HttpMethod method,
+        string requestUri,
+        CancellationToken cancellationToken, HttpContent? body = null)
+    {
+        if (method == HttpMethod.Get)
+            return await client.GetAsync(requestUri, cancellationToken);
+        if (method == HttpMethod.Post)
+            return await client.PostAsync(requestUri, body, cancellationToken);
+        if (method == HttpMethod.Delete)
+            return await client.DeleteAsync(requestUri, cancellationToken);
+        if (method == HttpMethod.Put)
+            return await client.PutAsync(requestUri, body, cancellationToken);
+
+        throw new NotImplementedException();
+    }
+
     /// <summary>
     /// Tries to retrieve a valid <see cref="Models.Jwt.JsonWebTokenPair" />.
     /// </summary>
     /// <param name="cancellationToken">An optional token to signal cancellation of the operation.</param>
     /// <returns>
-    /// A valid <see cref="Models.Jwt.JsonWebTokenPair" /> if the operation was successful.
-    /// Otherwise returns null.
+    /// A <see cref="NordigenApiResponse{TResult,TError}"/> containing the <see cref="JsonWebTokenPair"/> or
+    /// the error of the operation.
     /// </returns>
-    private async Task<JsonWebTokenPair?> TryGetValidTokenPair(CancellationToken cancellationToken = default)
+    private async Task<NordigenApiResponse<JsonWebTokenPair, BasicResponse>> TryGetValidTokenPair(
+        CancellationToken cancellationToken = default)
     {
         // Request a new token if it is null or if the refresh token has expired
         if (JsonWebTokenPair == null || JsonWebTokenPair.RefreshToken.IsExpired(TimeSpan.FromMinutes(1)))
         {
             var response = await TokenEndpoint.GetTokenPair(cancellationToken);
-            TokenPairUpdated?.Invoke(this, new TokenPairUpdatedEventArgs(response.Result));
-            return response.Result;
+            if (response.IsSuccess)
+                TokenPairUpdated?.Invoke(this, new TokenPairUpdatedEventArgs(response.Result));
+
+            return response;
         }
 
         // Refresh the current access token if it's expired (or valid for less than a minute)
@@ -139,15 +174,21 @@ internal async Task<NordigenApiResponse<TResponse, TError>> MakeRequest<TRespons
             var response = await TokenEndpoint.RefreshAccessToken(JsonWebTokenPair.RefreshToken, cancellationToken);
             // Create a new token pair consisting of the new access token and existing refresh token
             var token = response.IsSuccess
-                ? new JsonWebTokenPair(response.Result!.AccessToken, JsonWebTokenPair.RefreshToken,
+                ? new JsonWebTokenPair(response.Result.AccessToken, JsonWebTokenPair.RefreshToken,
                     response.Result!.AccessExpires, JsonWebTokenPair.RefreshExpires)
                 : null;
-            TokenPairUpdated?.Invoke(this, new TokenPairUpdatedEventArgs(token));
-            return token;
+            var tokenPairResponse = new NordigenApiResponse<JsonWebTokenPair, BasicResponse>(response.StatusCode,
+                response.IsSuccess, token, response.Error);
+
+            if (token is not null)
+                TokenPairUpdated?.Invoke(this, new TokenPairUpdatedEventArgs(token));
+
+            return tokenPairResponse;
         }
 
-        // Token pair is still valid and can be returned
-        return JsonWebTokenPair;
+        // Token pair is still valid and can be returned - wrap in NordigenApiResponse
+        return new NordigenApiResponse<JsonWebTokenPair, BasicResponse>(HttpStatusCode.OK, true, JsonWebTokenPair,
+            null);
     }
 }
 
@@ -159,13 +200,13 @@ public class TokenPairUpdatedEventArgs : EventArgs
     /// <summary>
     /// The updated <see cref="Models.Jwt.JsonWebTokenPair" />.
     /// </summary>
-    public JsonWebTokenPair? JsonWebTokenPair { get; set; }
+    public JsonWebTokenPair JsonWebTokenPair { get; set; }
 
     /// <summary>
     /// Creates a new instance of <see cref="TokenPairUpdatedEventArgs" />.
     /// </summary>
     /// <param name="jsonWebTokenPair">The updated <see cref="Models.Jwt.JsonWebTokenPair" />.</param>
-    public TokenPairUpdatedEventArgs(JsonWebTokenPair? jsonWebTokenPair)
+    public TokenPairUpdatedEventArgs(JsonWebTokenPair jsonWebTokenPair)
     {
         JsonWebTokenPair = jsonWebTokenPair;
     }