1) In your business manager, go to ‘Brand safety’ and verify the domain name.
2) You will have to ‘add’ your website URL without ‘/…’ e.g.: netvisibility.com
3) Either follow the instructions from Facebook onto your website OR If you have a web developer send these to them and the Facebook TXT record (this is in step 2 below and will start with ‘Facebook-domain-verification=…’