Be happy together.
The correct answer is given as: Buďte spolu šťastní.
Is "Buďte šťastní spolu." really incorrect with just this small switch in word order?
Still not accepted after two years. Reported it now.
No need to report it. As VladaFu pointed out, it sounds bizarre to stress the "spolu" instead of "šťastní", so we won't accept it.
How about stressing that they should be happy together rather than happy d separately? :)