Facebook defines branded content (also known as "Handshake") as a creator or publisher's content that features or is influenced by a business partner for an exchange of value. In short, you can tag a third-party page to your post to show that you're collaborating with that page.
Getting started with branded content
For a creator to be able to tag a business partner to a post, that business partner must have page approvals turned on and added the creator as an approved partner. Read more in Facebook Ads Help Center.
How to tag a business partner in Smartly.io?
When you are creating a new creative you can add the branded content tag by inserting the partner page into the field shown below. If you don't know your partner page ID, please contact our support chat.
How to use branded content that is shared with your page or business?
When you are creating a new ad, and you want to boost a post that was created using Facebook's Branded Content tool, the first thing to check is that your business was given permission when the post was created. At the moment, boosting posts that your Facebook page is tagged in can only be done via Branded Content tool on Business Manager.
Also keep in mind that the pages you tag will be notified. Business partners will be able to view the post's metrics and use it to create ads. If you promote the posts then the tagged business partners can see ad spend and CPM metrics.
Branded Content in Facebook Ads Help Center
Can my Page access the branded content tool and post branded content?