The short answer
An active team pool is one credit budget shared by owners, administrators and members. Viewers cannot spend it. Further invitations do not increase the budget. For example, if one person uses 100 credits and another uses 50 from a pool of 5,000, the team has 4,850 left. The pool must be set up, its period must still be running and your membership must exist. An Enterprise badge or creating a team alone does not guarantee an active pool. If it is missing, have the setup checked.