docs: add plain objects troubleshooting page (#2364)

content/docs/08-troubleshooting/03-common-issues/09-client-stream-error.mdx

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+---
+title: Server Action Plain Objects Error
+description: Troubleshooting errors related to using AI SDK Core functions with Server Actions.
+---
+
+# "Only plain objects can be passed from client components" Server Action Error
+
+## Issue
+
+I am using [`streamText`](/docs/reference/ai-sdk-core/stream-text) or [`streamObject`](/docs/reference/ai-sdk-core/stream-object) with Server Actions, and I am getting a `"only plain objects and a few built ins can be passed from client components"` error.
+
+## Background
+
+This error occurs when you're trying to return a non-serializable object from a Server Action to a Client Component. The streamText function likely returns an object with methods or complex structures that can't be directly serialized and passed to the client.
+
+## Solution
+
+To fix this issue, you need to ensure that you're only returning serializable data from your Server Action. Here's how you can modify your approach:
+
+1. Instead of returning the entire result object from streamText, extract only the necessary serializable data.
+2. Use the [`createStreamableValue`](/docs/reference/ai-sdk-rsc/create-streamable-value) function to create a streamable value that can be safely passed to the client.
+
+Here's an example that demonstrates how to implement this solution: [Streaming Text Generation](/examples/next-app/basics/streaming-text-generation).
+
+This approach ensures that only serializable data (the text) is passed to the client, avoiding the "only plain objects" error.