diff --git a/PcgsInvUi/Services/PcgsClient.cs b/PcgsInvUi/Services/PcgsClient.cs
index b913f64..3e2af44 100644
--- a/PcgsInvUi/Services/PcgsClient.cs
+++ b/PcgsInvUi/Services/PcgsClient.cs
@@ -1,19 +1,16 @@
 using System;
+using System.Collections.Generic;
 using System.Net.Http;
 using System.Net.Http.Headers;
 using System.Threading.Tasks;
 using PcgsInvUi.Models;
 using System.Text.Json;
+using DynamicData.Kernel;
 using ReactiveUI;
 
-
 namespace PcgsInvUi.Services;
 
-/// <summary>
-/// Provides an interface into the PCGS Public API.
-/// </summary>
 public class PcgsClient : ReactiveObject {
-    
     public int NumApiRequests {
         get => _numApiRequests;
         set => this.RaiseAndSetIfChanged(ref _numApiRequests, value);
@@ -24,12 +21,12 @@ public class PcgsClient : ReactiveObject {
     private int _numApiRequests;
 
     public PcgsClient(string apiKey) {
-        // I'd like to be able to test the API key upon initialization.
+        // _apiKey = apiKey;
         _apiKey =
             "E8xivTVN_k4Q8ubk8Xv_uU11U91WX0wDht4S4m4BAf2HPmKnGrZ0J2f9nccM7Ns1VkGoT1SXYR74I7aNaMKqXlJGEy3oobseKV0nGiqu1IKvFkOTVjhV37SWUVExSDFMC6FLzs7xJQIHwkcxr5JFOQNmc4ZytEh_-hmCN3NL-z0fEk98tzBmPJ_F7bq_xNru86QMD2A9yalu_dWe-lCysfyE2bCA2EDqwvWenRYf-0XnNtp6qlxxCMlCd-TDqqRKLC3qefCwpXSemwBiNSP5gbC9pwcKrZugkruuJ0nyxxThZymm";
     }
 
-    public async Task<Coin> GetCoinFactsByGrade(int pcgsNumber, string grade, bool plusGrade = false) {
+    public async Task<Coin?> GetCoinFactsByGrade(int pcgsNumber, string grade, bool plusGrade = false) {
         Coin newCoin = null;
         using (HttpClient client = new HttpClient()) {
             var gradeParam = GetGradeFromString(grade);
@@ -42,15 +39,12 @@ public class PcgsClient : ReactiveObject {
             Console.WriteLine("Got response.");
 
             if (response.IsSuccessStatusCode) {
-                // TODO Check for errors indicated by a successful response.
                 string jsonResponse = await response.Content.ReadAsStringAsync();
                 newCoin = ParseJsonResponse(jsonResponse);
                 Console.WriteLine("Coin created.");
             }
             else {
-                // TODO Throw HTTP exception.
-                Console.WriteLine("Error getting coin.");
-                
+                Console.WriteLine($"Error: {response.StatusCode} - {response.ReasonPhrase}");
             }
         }
 
@@ -65,46 +59,27 @@ public class PcgsClient : ReactiveObject {
 
     // TODO Will eventually create the other methods that are included in the Public API.
 
-    private Coin ParseJsonResponse(string json) {
+    private Coin? ParseJsonResponse(string json) {
         Console.WriteLine(json);
-        Coin newCoin = JsonSerializer.Deserialize<Coin>(json);
-        Console.WriteLine($"New Coin has pcgs number {newCoin.PCGSNo}");
-
-        string test = JsonSerializer.Serialize(newCoin);
-        Console.WriteLine(test);
+        // TODO Check for errors in the response
+        if (json.Contains("\"ServerMessage\":\"No data found\"")) throw new CoinNotFoundException("No coin found with that PCGS number.");
+        if (json.Contains("\"IsValidRequest\":true")) throw new InvalidRequestFormatException("Invalid request format.");
 
+        var newCoin = JsonSerializer.Deserialize<Coin>(json);
         return newCoin;
     }
 }
 
-/// <summary>
-/// Thrown when the API response indicates that the request was invalid.
-/// Generally used when the request was formatted incorrectly.
-/// </summary>
-public class InvalidRequestException : Exception {
-    public InvalidRequestException() { }
-    public InvalidRequestException(string message) : base(message) { }
-    public InvalidRequestException(string message, Exception inner) : base(message, inner) { }
+// Exception for invalid request format
+class InvalidRequestFormatException : Exception {
+    public InvalidRequestFormatException() { }
+    public InvalidRequestFormatException(string message) : base(message) { }
+    public InvalidRequestFormatException(string message, Exception inner) : base(message, inner) { }
 }
 
-/// <summary>
-/// Thrown when the API response indicates that the coin was not found.
-/// Generally used when the PCGS number and grade combo that was requested does not exist in the PCGS database.
-/// </summary>
-public class CoinNotFoundException : Exception {
+// Exception for no coin found
+class CoinNotFoundException : Exception {
     public CoinNotFoundException() { }
     public CoinNotFoundException(string message) : base(message) { }
     public CoinNotFoundException(string message, Exception inner) : base(message, inner) { }
-}
-
-/// <summary>
-/// Thrown when the API returns an HTTP error 401.
-/// Generally indicates that the API key is invalid.
-/// </summary>
-public class ApiAuthorizationException : Exception {
-    public ApiAuthorizationException() { }
-    public ApiAuthorizationException(string message) : base(message) { }
-    public ApiAuthorizationException(string message, Exception inner) : base(message, inner) { }
-}
-
-public 
+}
\ No newline at end of file
diff --git a/PcgsInvUi/ViewModels/MainWindowViewModel.cs b/PcgsInvUi/ViewModels/MainWindowViewModel.cs
index 4bc71af..c4256e8 100644
--- a/PcgsInvUi/ViewModels/MainWindowViewModel.cs
+++ b/PcgsInvUi/ViewModels/MainWindowViewModel.cs
@@ -41,6 +41,7 @@ public class MainWindowViewModel : ViewModelBase {
     public Interaction<DeleteWindowViewModel, Boolean> ShowDeleteWindow { get; }
     public ReactiveCommand<Unit, Unit> ExportCommand { get; }
     public Interaction<Unit, Uri> ShowExportWindow { get; }
+    public Interaction<Unit, Unit> ShowErrorWindow { get; }
 
     private ViewModelBase _sideContent;
     private Coin? _selectedCoin;
@@ -55,6 +56,9 @@ public class MainWindowViewModel : ViewModelBase {
         DisplayedList = ConnectedCoinDatabase.Collection;
         TotalValue = DisplayedList.Sum(x => x.TotalPrice);
         
+        // Set up the ability to show the error window.
+        ShowErrorWindow = new Interaction<Unit, Unit>();
+        
         // Set up the ability to open the delete window.
         ShowDeleteWindow = new Interaction<DeleteWindowViewModel, bool>();
         var deleteEnabled = this.WhenAnyValue(x => x.SelectedCoin)
@@ -89,7 +93,15 @@ public class MainWindowViewModel : ViewModelBase {
         // This is the same as the above, but with a different syntax.
         newViewModel.OkCommand
             .Subscribe(async requestStructure => {
-                ConnectedCoinDatabase.CreateCoin(requestStructure.Item1, requestStructure.Item2, requestStructure.Item3);
+                try {
+                    ConnectedCoinDatabase.CreateCoin(requestStructure.Item1, requestStructure.Item2,
+                        requestStructure.Item3);
+                }
+                catch (Exception e) {
+                    // TODO Error handling - create a popup window.
+                    Console.WriteLine(e.Message);
+                }
+                // TODO Clear the text boxes.
             });
 
         // Change TotalValue anytime SelectedCoin.TotalPrice changes.
diff --git a/PcgsInvUi/Views/MainWindow.axaml.cs b/PcgsInvUi/Views/MainWindow.axaml.cs
index 7f80fb8..445fa4e 100644
--- a/PcgsInvUi/Views/MainWindow.axaml.cs
+++ b/PcgsInvUi/Views/MainWindow.axaml.cs
@@ -53,4 +53,11 @@ public partial class MainWindow : ReactiveWindow<MainWindowViewModel> {
             throw new Exception("User cancelled the file picker.");
         }
     }
+    
+    public async Task ShowErrorWindowAsync(InteractionContext<Unit, Unit> interaction) {
+        var window = new ErrorWindow();
+        window.DataContext = interaction.Input;
+
+        await window.ShowDialog(this);
+    }
 }
\ No newline at end of file