https://www.ivisa.com/grenada-travel-authorization

A Grenada Travel Authorization is a legally valid passport issued from the Grenada government. It doesn't contain any nation information but includes an entrance destination and request. Permission to travel out of the territorial waters is only allowed upon demonstration of a Grenada Travel Authorization. The authorization, which functions as a ticket for the right of passage to the Grenada National Parks, can be obtained from the authorized tourist office.