When working with a Facebook Ads agency you will have to give them access to your Facebook Page so they can run ads on your behalf.
Here are the instructions on how to do so.
Log into your Facebook Business Manager Account
Click on the “Business Settings” button in the top right-hand corner
- Choose pages in the left menu
- Click on the “Assign Partner” button on the right
Click on the “Connect your page using your Partners Assigned Partner ID instead” link
Choose Page Advertiser from the dropdown
Enter your Partner’s business ID