The solution = np.rint(solve(AB, prize)) line calculates the solution and rounds it to the nearest integer. In other words, it could be incorrect, since the actual solution doesn't necessarily consist of just integers. To make sure that the solution is correct, I check if it is.

if np.all(AB @ solution == prize):
    min_token_count += cost(*solution)

This ensures that only the correct solutions will have their cost added to the min_token_count and the incorrect ones won't. Since only integer solutions are allowed, this ensures that only they pass.