About Nathan saying he didn’t receive the recipe, when you send the recipe it should show “SYSTEM MESSAGE YOU SUBMITTED A RECIPE”. If that message didn’t appear, then for some reason the AI didn’t call the function to use the recipe, it might be a bug.
(SPOILERS BELOW)
But once you discover the plot it’s no longer necessary to send him the recipe.
The game has two mysteries to uncover: why you are there and what that place actually is.
After collecting all the toys you receive an email explaining why you are there. In the emails you have sent you also discover that there is a hidden password to unlock deleted emails. Once you use the password you will find out in those deleted emails what that place really is, what happened to the previous subject and why Nathan is still alive. It is a narrative driven story and there is only one ending.