This post will show you how to claim your Facebook ad account inside your Business Manager.
You’ll need to have a Business Manager account. If you don’t have one, go to: business.facebook.com to create one.
Go to Business Manager Settings to claim the ad account
Go to Advert Accounts (sometimes called: Ad Account)
Claim your Ad Account
You will then be prompted to enter the Ad Account ID here:
You can find your Ad Account ID in the URL params when you are on the ad account. The account id will be the numbers after ?act=XXXXXXXXXXX in the URL.
You should now have your ad account assigned to your business manager!