Hello Kedar
What functionality are you using in APO?
To include stock types in the planning book you have to change the stock types in the Stock Category Group in the SNP tab of the location masterdata in APO. You maintain this with 'Maintain Category Groups' in customizing. If left black the default is ST1 and if you are making changes you should create a new category group, e.g.: ZST.
Kind regards
Michael