Do I need a Meta Developers account to connect WhatsApp?

No. You connect from your panel through Meta’s guided signup: in Chatbot → Channels → WhatsApp you press “Connect Account”, choose how to connect and Meta’s window opens, where you log in with your Facebook account and pick or create your business portfolio. You don’t need a developer account or any invitations.

All the steps, with screenshots, are in the guide Connect WhatsApp Business to CitaFlow.