can I add multiple account on just 1 billed account

I run an agency with more than four clients and am interested in using ManyChat for all of them. Ideally, I would like to manage their social media through my ManyChat account without asking for payment from them, essentially offering this service as a "gift." Is it possible to add all their Instagram and Facebook profiles under my agency's ManyChat account, or do I need to create a separate account for each client and have them pay for it?