Please follow these steps:
Download a Facebook build from your Playground account (click on the 3 dots at the end of your Playable in PG, select Export, choose Facebook)
Navigate to the Facebook playable preview tool.
Drag in your index.html file or find it manually.
You may now test the playable in the preview, and change the resolution.
If the playable is incorrectly formatted or over the file size limit, you will see an error.
You can read more about this here.