If you've changed which form your popup displays, you'll notice that the preview method above no longer appears to work. Instead, when you preview your popup, you'll only get the shortcode for your form. To fix this, you'll need to temporarily change your Campaign's Publish Status. For example, if your Publish Status is set to Draft, change it to Publish. Your form will be refreshed and loaded correctly within your OptinMonster popup. If you're not ready for your popup to be live, be sure to check that your Publish Status is set to Draft when you're done previewing.