What to expect
‘Boat to Pacaya Samiria’ sounds like a single connection. Ask about the actual journey instead: where do you board, register and sleep? The booking should also explain who arranges access and how you return. Save those details offline with the contact of the person who will receive you.
How it fits into a journey
Connect the boat arrangement to the Iquitos–Nauta road transfer. Leave room after the return journey before flying onwards.