To set up your cover image:
- When editing your form, go to Configure > Details
- Upload an image to ‘Cover Image’ (recommended size is 600 x 400 pixels)
If the form has been shared to Facebook before, you may need to clear Facebook’s cache. To do this, go to https://developers.facebook.com/tools/debug/ and enter in the URL of the form. Click the “Debug” button, and then on the next page, click the “Scrape again” button.