If you manage hundreds or thousands of small businesses and want to offer them ads buying within your website or platform, Facebook has a solution for you. We have built a set of APIs that allow you to on board your clients to Facebook advertising with great ease. Using this solution you can create Ad accounts for your clients, manage their ad campaigns and pay for any ads created on their behalf directly to Facebook. This solution allows our partners to build new ads buying experiences within their website or platform.
When using the two-tier business manager solution, you can create a Child Business Manager(CBM) on behalf of your client using their user access token and a Facebook page that is owned by them. They do not have access to the Client Business manager (CBM) by default but you have complete access to the child BM and can chose to give your clients read only permission if they have a use case for it. Your clients doesn't have access to the new CBM and its ad account unless you explicitly grant them access. Some additional notes about this setup:
For more information regarding these APIs you can visit the Marketing Docs on on boarding here, https://developers.facebook.com/docs/marketing-api/business-manager-api/business-onboarding