Yes, unless it is already obvious. Art. 50(1) requires that people interacting with an AI system are informed they are interacting with AI, and Art. 50(5) says that information must reach them at the latest at the time of the first interaction, in a clear and distinguishable manner. The duty formally sits on the provider of the chatbot, but you are the business the customer sees, so in practice you want the notice visible on every channel the assistant runs on.
The "obvious" exemption is judged from the point of view of a reasonably well-informed person — your average customer, not you. The full guide to chatbot disclosure walks through what counts.