If there's a message box pops up says "This product cannot be entered manually" when you click the product button on your task pad, please follow this procedures below to resolve the problem.  

Procedure

1. Sign in to your back office and go to Admin-> Task Pad then select the POS Default task pad.
2. Select the Product button and click the edit button in the Command section 
3. Please click the Properties and check the "Can Add on Searchable" then change the drop down settings from false to true and click the submit button. 
4. Then click the Save button on the upper right corner of the page.
5.  Then sync your POS, please check this knowledge base link on how to sync your POS. Help! I made a change to my Discount/Loyalty Program/Receipt/etc. and it isn't working on the POS. : RITE Help Desk (freshdesk.com) 

References