If any of your posts get this kind of error when using Custom FB Branding, please follow the following steps:
- Log in to your Facebook account
- Click on Settings from the drop-down arrow from the header.
- Click on Developers from the bottom.
- From the My Apps drop down, select the custom app you used for the social media profile which generated this error.
- Click on Settings -> Advanced from the side bar menu.
- Scroll down till you reach the Client Token section.
- Make sure Require App Secret is turned to "No"
Now you can reshare your post and it will share perfectly fine!