If achieving happiness is not the goal of moral behavior

what is?

The correct answer is Universal conduct, based on Universal values

Happiness is the state in which a rational being is found in the world for whom, in all his existence, everything goes according to his desire and will; consequently, it presupposes the agreement of nature with all the ends of this being, and simultaneously with the essential foundation of determining its will. Now the moral law, as a law of freedom, obliges by means of foundations of determination, which must be entirely independent of nature and its agreement with our faculty of desire (as an engine). However, the rational agent that acts in the world is not simultaneously the cause of the world and of nature itself. Thus, in the moral law, there is no basis for a necessary connection between morality and happiness, provided with it, in a being that, being part of the world, depends on it; this being, precisely for this reason, cannot voluntarily be the cause of this nature nor, as far as happiness is concerned, make it, by its own strength, perfectly coincide with its own practical principles.

explanation:

may i ask what challenges?