What is it?
Very often campaigns ask for a preview from you after your request has been accepted. It's for brands to see your content before you upload it in order to check whether it's okay for them. So it's very important to check whether a campaign asks for a preview or not!
What should you do?
The moment you got accepted you will be notified, and you can start working on your preview (if the brand indicated that they need it). You can upload previews by clicking “Upload preview” under “Content” on the menu bar, or "Proposed" in the app. You have to select the photo or video from your device and hit enter.
What to do after uploading the preview?
Always wait for the brand's answer to your preview. After they have accepted the preview you can upload the content to your social site. In case a brand does not answer you try writing them directly.