The government is maybe paying a bounty for books because they want to destroy books. Idk if they still are doing that. The book store is giving some of its profits to buy a truck. It's all roundabout nonsense economics tied into a bizarre propaganda program. "It is patriotic to give money to the war effort. It is patriotic to destroy books. Thus destroying books is part of the war effort. Destroy all Russian language media and speak only Ukrainian, this is how you do your part in winning the war."

Nationalism doesn't make a lot of sense under even the lightest analysis, and this is no exception.

It's highly unlikely enough Ukrainians are engaged in this convoluted scheme for the government to generate any kind of meaningful revenue. This is likely just a logically stupid propaganda campaign to boost morale, and when some western country sends Ukraine trucks, they'll thank the citizens for sacrificing their hard earned cash for the trucks lol.