Is "Tak du og farvel" structurally incorrect?
For me it sounds unnatural.
can this be "tak hej hej" as well?
Maybe "tak og hej hej".
It should actualy be takker og farvel
What is the difference between "tak" and "takker"?
As far as I know Tak is a whole phrase on its own
What is the difference between "tak" and "tak skal du have"?
It is the same, it's just said differently