Antonio and his children run this out of Leticia with an indigenous family who grew up on the river. Boats leave every day at 9:30 in the morning and it is two hours up the Yavarí, the blackwater tributary that forms the Peru–Brazil border, to their lodge at Zacambú.
They publish the lodge's GPS coordinates on the website, which almost no Amazon operator does and which tells you something about how they expect to be checked.
Four days is the standard trip. Book on WhatsApp; there is no email address on the site.