Debit lines on same invoice as charge lines

Customer orders allow sales items and charge types. The value on the charge types can be + or -.   Charge types can represent nearly anything including various flavors of adjustments. It appears that the integration may need some attention. 

Is this the only workaround there is to use charges ?
I need to understand why IFS allows the debit lines on an SCO order from the service contract module , but on a normal order this is not allowed.
Can I create an SCO order just from an invoice file instead of the call from service contract module ?
 

As Thomas has said, IFS allows order lines and charge lines on the same customer order and it is the most common case how charges are used.  Maybe there are some restrictions just for the SCO order type. In that case you need to create a new order type or use the NO (normal) order type.

I am not sure that I am able to explain properly.

Today I am able to create an SCO order from the service contract module with for example 3 order lines
2 of the lines has a plus quantity, which give a plus amount
1 of the lines has a minus quantity, which give a minus amount
And the total amount of the order is plus

Now I need to create the order from an integration file from another system.
And now I am not allowed to created this kind of order with these specific lines.

I will not be using charges, because that is not an order line and I need this to be an order line.

So my question is: Why am I not allowed to create a simular order like the SCO order, just with the integration file instead of the call from inside IFS service contract module.

It’s not possible to have negative quantities or values on order lines. You need to use charges with negative values. I don’t have much experience with SCO orders but that sounds to me like a functionality that is hardcoded for the SCO order type (if not a customization/modification even).