Add Xamarin troubleshooting (getsentry#3878)

src/platforms/dotnet/guides/xamarin/index.mdx

@@ -49,6 +49,41 @@ By calling it, the SDK will not automatically Cache your events and they might b
 
 Disables the automatic Logging of internal Warnings that comes from Xamarin Forms.
 
+## Troubleshooting
+
+If you need help solving issues with your Sentry's Xamarin SDK, you can read the edge cases documented here. If you need additional help, you can view our forums, and customers on a paid plan may also contact support.
+
+### Offline Caching Information 
+
+For users on Xamarin iOS, offline caching may cause this tricky issue.
+
+#### Event/Transaction Capture - `Failed to send cached envelope: System.MissingMethodException: Method not found: System.Text.Json.JsonDocument`
+
+If this message displays when capturing an event or transaction on your debug window, manually edit your platform `csproj`:
+
+1. Close your IDE
+2. Open your iOS `.csproj` with a text or xml editor
+3. Add the following NuGet reference:
+```xml
+    <PackageReference Include="System.Memory" IncludeAssets="None">
+      <Version>4.5.4</Version>
+    </PackageReference>
+```  
+<Note>
+
+It's important to add the `IncludeAssets` as `None`, otherwise this fix will not work.
+
+</Note>
+
+4. Save and open your IDE
+5. Wait for the IDE to restore the packages. Once finished, try to capture an exception or transaction
+
+
+Another way to validate if the problem is happening on an iOS project, is by adding the following code to your iOS project to check if there's a conflict:
+```csharp
+    _ = new byte[2].AsMemory();
+```
+
 ## Samples
 
 - An [example](https://github.com/getsentry/sentry-xamarin/tree/main/Samples) using Xamarin Forms and most of the SDK features. (**Android, iOS, UWP**)