Business Login is the process for generating Page access tokens not bound to a User access token. These Page access tokens are dependent on a System User, and so they remain valid through changes in personal accounts. To make these tokens more resilient, they are not subject to an expiration date.
A direct business, a business that holds the ownership of its Pages and apps, can set up a stable Page access token through a System User.
If your app is supporting Pages that are owned by other businesses, use the Business Login flow. This flow is recommended for direct businesses only.
Before you generate a Page access token based on a System User, you need the following:
/<PAGE_ID>?fields=access_tokenendpoint with the system user access token above.