Added missing initialization of ConvexReactClient in Convex integrati…

docs/guides/development/integrations/databases/convex.mdx

@@ -148,7 +148,7 @@ With [Convex](https://www.convex.dev/), you can build a backend with a provided
     <Tab>
       The following example demonstrates how to configure Clerk and Convex's providers. Clerk's [`useAuth()`](/docs/reference/hooks/use-auth) hook must be passed to Convex's `<ConvexProviderWithClerk>` and Clerk's `<ClerkProvider>` must be wrapped around it.
 
-      ```ts {{ filename: 'src/main.tsx', mark: [[5, 7], 19, 21] }}
+      ```ts {{ filename: 'src/main.tsx', mark: [[5, 7], 25, 27] }}
       import React from 'react'
       import ReactDOM from 'react-dom/client'
       import App from './App.tsx'
@@ -164,6 +164,12 @@ With [Convex](https://www.convex.dev/), you can build a backend with a provided
         throw new Error('Add your Clerk Publishable Key to the .env file')
       }
 
+      if (!process.env.VITE_CONVEX_URL) {
+        throw new Error('Missing VITE_CONVEX_URL in your .env file')
+      }
+
+      const convex = new ConvexReactClient(process.env.VITE_CONVEX_URL)
+
       ReactDOM.createRoot(document.getElementById('root')!).render(
         <React.StrictMode>
           <ClerkProvider publishableKey={PUBLISHABLE_KEY} afterSignOutUrl="/">