Kant's view about freedom of the will, […] is one of the most unstable areas in his philosophy. It is a topic he frequently revisited, never saying quite the same thing he ever said before. Kant's theory of freedom, and especially the idea that we are free only in the intelligible world beyond nature, has also been the chief stumbling block to the acceptance of his moral philosophy. The scandal has only increased with the passage of time, as fewer and fewer moral philosophers find it tolerable to burden morality with an extravagant supernaturalist metaphysics.

Kantian Ethics (2008) - Ch. 7. Freedom