Verify Your Domain in Business Manager.
Facebook has very recently, within the last few weeks, updated its policies and procedures surrounding ad creation and management. Domain verification is now an additional step that each business must complete in order to continue with running ads.
Verifying your business’s domain in Business Manager is a way to help Facebook know that you are connected to your business. Domain verification establishes which Business Manager account has the authority to configure and prioritize the 8 available conversion events for a given domain.
*Domain verification is mission-critical in order to run ads properly
Begin by going to Domains in the Brand Safety Section of Business Settings