Compare the settings if your schedule line category in VOV6 and you will see the difference.
Keep an eye on the box for availability
Picture Source: SAP SD Certification Questions
From the naming the first character stands for the document type C = sales order (A = inquiry, B = quotation), the second character defines the usage, e.g. N = no planning P = planning MRP V = planning Consumption based
CP means sales order MRP planning while CN means sales order no planning.