What counts as an active affiliate and affects my plan's limit?

An affiliate with the status Active means an affiliate with an active/approved account in your program i.e. an affiliate who is actively promoting your store to potential customers.

Also, note the following affiliate status in Affiliatly:

• Not approved (orange background):
  Not counted towards your plan's limit
• Blocked (red background):
  Counted towards your plan’s limit, as we are considering blocked affiliates as a temporary status

If you need to free up some space in your current plan, you have to either disapprove affiliates or delete their account. You can do both of these actions in the Affiliate Details window on the Affiliate page. Just click the ⚙️ on the very right of the affiliate.