No.30 of 52 can be found here:

US | https://www.amazon.com/dp/B0HP7Q9MNS
DE | https://www.amazon.de/dp/B0HP7JH8GZ

When the alien crew of the Zygnon-7 lands on a radiation-scorched Earth, they discover a mysterious box buried deep beneath the surface. Its contents must be of immeasurable value—after all, the last humans hid it before the apocalypse. But what the aliens discover inside puts their understanding of human intelligence to the ultimate test.

It’s free until Friday. Please leave me a review on Amazon if you liked the story. Thanks.