In order to use the latest version of the Facebook share dialogue, Facebook requires you to set up an app associated with your site.
Luckily, this is a lot easier to do than it might first seem. It does require that you have a Facebook account, though.
Log in to your Facebook account and go to https://developers.facebook.com/apps/. On this page, you'll see a button that says "Add New App":
Click on this button to get to the next step.
In the modal window that pops up, select the "Website" option:
You'll be asked to enter a name for your new app. This can be any name you want it to be, e.g. "Sharing for SiteName". Click on the button to create your app ID:
Next, select "Apps for Pages" as the category (you can also select any other category, it doesn't matter for this setup) and then click on the "Create App ID" button:
On the next screen, scroll down until you find the field to enter your site's URL. As you probably guessed, this is where you add the URL of the site you want to use the Facebook share buttons on:
Click on the "Next" button.
Scroll back to the top of the page and go to "My Apps":
Either click on your app in the drop-down that appears or select it from the screen that appears when you click on "My Apps".
Next, go to "Settings", where you need to enter your site's domain and a contact email address in the corresponding fields:
Save your changes and then select "Status & Review" in the sidebar. Here, you can set your app live to start using it:
Go back to the app dashboard and copy the App ID from here:
In Thrive Content Builder, add the social sharing element to your content and choose "Social Options" from the element options in the builder:
With the Facebook share options selected (note that if you deactivate the Facebook button, this tab will not be visible), enter the App ID in this field and click on the "Validate" button:
With this, your app setup and integration are complete and you can use the Facebook "Feed Dialog" style sharing on any page of your website.