Fix with mux video example (#37434)

* fix: On error upchunk dispatches an object

* chore: Typo on contribution guide, `unverfied`

* Update contributing.md

Co-authored-by: Lee Robinson <me@leerob.io>
Co-authored-by: JJ Kasper <jj@jjsweb.site>

contributing.md

@@ -323,7 +323,7 @@ Issues are opened with one of these labels:
 
 - `template: story` - a feature request, converted to an [💡 Ideas discussion](https://github.com/vercel/next.js/discussions/categories/ideas)
 - `template: bug` - unverified issue with Next.js itself, or one of the examples in the [`examples`](https://github.com/vercel/next.js/tree/canary/examples) folder
-- `template: documentation` - feedback for improvement or unverfied issue with the Next.js documentation
+- `template: documentation` - feedback for improvement or an unverified issue with the Next.js documentation
 
 In case of a bug report, a maintainer looks at the provided reproduction. If the reproduction is missing or insufficient, a `please add a complete reproduction` label is added. If a reproduction is not provided for more than 30 days, the issue becomes stale and will be automatically closed. If a reproduction is provided within 30 days, the `please add a complete reproduction` label is removed and the issue will not become stale anymore.
 

examples/with-mux-video/components/upload-form.js

@@ -62,7 +62,7 @@ const UploadForm = () => {
     })
 
     upload.on('error', (err) => {
-      setErrorMessage(err.detail)
+      setErrorMessage(err.detail.message)
     })
 
     upload.on('progress', (progress) => {