The Pay Type field in AP Unapproved Invoice Entry, Lines section, Info tab.
Specify the pay type for this item. If you are using pay categories (flag in AP Company Parameters), defaults the pay from this line's pay category based on the line type. The pay type used for each line type is as follows:
Job lines - Use the Job pay type
Inv, Exp, Equip, and EM Work Order lines - Use the Expense pay type
PO lines - Use the pay type assigned to the PO item.
SL lines - Use the Subcontract pay type
SM Work Order lines - Use the SM Work Order pay type
If you allow pay type overrides (flag in AP Company Parameters), you may override the default.