Добавил класс для представления сообщения

AMessanger.Core/AMessanger.Core.csproj

@@ -8,6 +8,7 @@
 
   <ItemGroup>
     <PackageReference Include="Microsoft.AspNetCore.SignalR" />
+    <PackageReference Include="Newtonsoft.Json" />
   </ItemGroup>
 
 </Project>

AMessanger.Core/Hubs/ChatHub.cs

@@ -1,3 +1,4 @@
+using AMessanger.Core.Models;
 using Microsoft.AspNetCore.SignalR;
 using Microsoft.Extensions.Logging;
 
@@ -5,9 +6,9 @@ namespace AMessanger.Core.Hubs;
 
 public class ChatHub(ILogger<ChatHub> logger) : Hub
 {
-    public async Task SendMessage(string user, string message)
+    public async Task SendMessage(Message message)
     {
-        logger.LogInformation($"{user}: {message}");
-        await Clients.All.SendAsync("ReceiveMessage", user, message);
+        logger.LogInformation($"{message.UserName}: {message.Content}");
+        await Clients.All.SendAsync("ReceiveMessage", message);
     }
 }

AMessanger.Core/Models/Message.cs

@@ -0,0 +1,8 @@
+namespace AMessanger.Core.Models
+{
+    public class Message(string userName, string content)
+    {
+        public string UserName { get; set; } = userName;
+        public string Content { get; set; } = content;
+    }
+}

Directory.Packages.props

@@ -5,6 +5,7 @@
   <ItemGroup>
     <PackageVersion Include="Microsoft.AspNetCore.OpenApi" Version="10.0.11" />
     <PackageVersion Include="Microsoft.AspNetCore.SignalR" Version="1.2.12" />
+    <PackageVersion Include="Newtonsoft.Json" Version="13.0.4" />
     <PackageVersion Include="Swashbuckle.AspNetCore" Version="10.2.3" />
   </ItemGroup>
 </Project>