Hi,

Inventory Part Planning Methods K, T and O are used to indicate that essentially the part is used for planning purposes. 

This means that it cannot manufactured or purchased, cannot be stocked and therefore cannot be sold as a Sales Part.

So the options are that you either need to change the Inventory Part Planning Method (but presumably that will have some consequences on the planning activities depending on your set up) or otherwise define your Sales Part as ‘non-inventory’.

I hope this helps.