I made it work

PcgsInvUi/ViewModels/ApiKeyViewModel.cs

@@ -1,5 +1,6 @@
 using ReactiveUI;
 using System.Reactive;
+using System;
 
 namespace PcgsInvUi.ViewModels;
 

PcgsInvUi/ViewModels/MainWindowViewModel.cs

@@ -39,23 +39,22 @@ public class MainWindowViewModel : ViewModelBase {
     public MainWindowViewModel(CoinDatabase coins, bool askForApiKey) {
         ConnectedCoinDatabase = coins;
         var newViewModel = new NewViewModel();
+        var apiKeyViewModel = new ApiKeyViewModel();
         // DisplayedList = CoinCollection = new ObservableCollection<Coin>(coins.GetItems());
         DisplayedList = ConnectedCoinDatabase.Collection;
         TotalValue = DisplayedList.Sum(x => x.TotalPrice);
 
         // Setup interaction to show ApiKeyWindow
+        apiKeyViewModel.OkCommand.Subscribe(apiKey => {
+            if (ConnectedCoinDatabase.TryInitApiClient(apiKey))
+                SidebarContent = newViewModel;  // Must assign this to the observable property.
+            });
+
         // Check if API key must be entered.
         if (askForApiKey) {
             Console.WriteLine("API key must be entered by user.");
             // Show the API key input view.
-            var apiKeyViewModel = new ApiKeyViewModel();
             _sideContent = apiKeyViewModel;
-            // Subscribe to the OkCommand in the ApiKeyViewModel.
-            apiKeyViewModel.OkCommand
-                .Subscribe(apiKey => {
-                    // Attempt to connect to the PCGS API and set view accordingly.
-                    if (ConnectedCoinDatabase.TryInitApiClient()) _sideContent = newViewModel;
-                });
         } else _sideContent = newViewModel;
         
         // Set up the ability to show the error window.
@@ -115,7 +114,8 @@ public class MainWindowViewModel : ViewModelBase {
                         break;
                 }
                 
-                // TODO Clear the text boxes.
+                // Clear the text boxes.
+                newViewModel.ClearText();
             });
         
         // Update TotalValue anytime a coin's quantity changes.

PcgsInvUi/ViewModels/NewViewModel.cs

@@ -40,9 +40,7 @@ public class NewViewModel : ViewModelBase {
             okEnabled);
 
         ClearCommand = ReactiveCommand.Create(() => {
-            PcgsNumber = "";
-            Grade = "";
-            Quantity = "";
+            ClearText();
         });
 
         // Initialize grade values for use in the view.
@@ -83,4 +81,13 @@ public class NewViewModel : ViewModelBase {
 
     public ReactiveCommand<Unit, (int, string, int)> OkCommand { get; }
     public ReactiveCommand<Unit, Unit> ClearCommand { get; }
-}
+
+    /// <summary>
+    /// Clears the text fields.
+    /// </summary>
+    public void ClearText() {
+        PcgsNumber = "";
+        Grade = "";
+        Quantity = "";
+    }
+}