One of the benefits of the procurement module in AX is the policies. These parameters allow you to control what happens in different processes. If you have just setup a new category and you can see it when you fill in a purchase order line but you can’t see it when you put in a requisition line then likely you need to review the category access policy rule that you can find in the purchasing policy.
Here is a quick overview.
AX2012 R2 CU11