In MPOS if you want to use categories, catalogs must be setup and validated. See the below TechNet article on setting up Catalogs
https://technet.microsoft.com/en-us/library/jj728723.aspx
See the following steps to create a new product and see the product as part of a category in MPOS:
USRT for the Houston store has a catalog called Men’s suits – My MPOS device is for the Houston store
Fashion category hierarchy – Dress Shirts
Create a new item in AX called “8888” this item is added to the Hierarchy Fashion > Menswear > Dress Shirts
Click OK and Edit the new item and add a selling price of 15.99
Find the assortment that the Houston store is using Retail > Common > Retail channels > Retail stores Select Houston Select View assortments Select Fab-base and click Edit Add the Fashion category to the assortment Click Publish
Go to Retail > Periodic > Process Assortments Run the Retail assortments job When finished, go to the Houston store and select View channel products You should see item 8888
Go to the Men’s suits catalog and edit Select Menswear > Dress Shirts Click Add under Products
Select Assortment Fab base Add item 8888
Click Validate catalog
Process the Retail catalog approval workflow
Ctrl+D to Developer workspace Expand Forms Type U Select Tutorial_WorkflowProcessor Right click and open
Click Start
When done publish the Catalog
Run the Products and Catalog job
When done Close MPOS if open and re-open.
The item will now show in the category