docs: adds live preview troubleshooting tips

docs/live-preview/frontend.mdx

@@ -187,3 +187,55 @@ For a working demonstration of this, check out the official [Live Preview Exampl
 - [Next.js App Router](https://github.com/payloadcms/payload/tree/main/examples/live-preview/next-app)
 - [Next.js Pages Router](https://github.com/payloadcms/payload/tree/main/examples/live-preview/next-pages)
 
+## Troubleshooting
+
+### Relationships and/or uploads are not populating
+
+If you are using relationships or uploads in your front-end application, and your front-end application runs on a different domain than your Payload server, you may need to configure [CORS](../configuration/overview) to allow requests to be made between the two domains. This includes sites that are running on a different port or subdomain. Similarly, if you are protecting resources behind user authentication, you may also need to configure [CSRF](../authentication/overview#csrf-protection) to allow cookies to be sent between the two domains. For example:
+
+```ts
+// payload.config.ts
+{
+  // ...
+  // If your site is running on a different domain than your Payload server,
+  // This will allows requests to be made between the two domains
+  cors: {
+    [
+      'http://localhost:3001' // Your front-end application
+    ],
+  },
+  // If you are protecting resources behind user authentication,
+  // This will allow cookies to be sent between the two domains
+  csrf: {
+    [
+      'http://localhost:3001' // Your front-end application
+    ],
+  },
+}
+```
+
+### Relationships and/or uploads disappear after editing a document
+
+It is possible that either you are setting an improper [`depth`](../getting-started/concepts#depth) in your initial request and/or your `useLivePreview` hook, or they're mismatched. Ensure that the `depth` parameter is set to the correct value, and that it matches exactly in both places. For example:
+
+```tsx
+// Your initial request
+const { docs } = await payload.find({
+  collection: 'pages',
+  depth: 1, // Ensure this is set to the proper depth for your application
+  where: {
+    slug: {
+      equals: 'home',
+    }
+  }
+})
+```
+
+```tsx
+// Your hook
+const { data } = useLivePreview<PageType>({
+  initialData: initialPage,
+  serverURL: PAYLOAD_SERVER_URL,
+  depth: 1, // Ensure this matches the depth of your initial request
+})
+```