Facebook Business Manager Access

Login to business.facebook.com

Click Partners

Click Ad Account
Select the Ad Account you'd like to provide us with access to
Click the Assign Partner link

Select the blue link at the bottom of the modal that says
Connect your ad account using your partner's business ID instead
Select the Advertiser role and enter our Facebook Business ID 357378441449902

Go to the Data Sources
Got to Catalogs
Create New Catalog if one hasn't been created
Once you've created a catalog then repeat the steps 

Go to the Pages
Repeat