Activate standard sum segment in INVOIC iDoc

Dear experts,

I am not sure if I am in the right board but I hope you can point me in the correct direction.

I have to map INVOICE02 to INVOIC EDIFACT format and in the sum segments of the EDIFACT message

I need a sum of all discounts.

Now in WE60 I checked the INVOIC02 structure and saw that in E1EDS01, QUALF='020' I get the sum of "allowances/charges".

But in my iDoc example I do not have an E1EDS01, QUALF='020'.

How can I "activate" or add that standard sum segment to my INVOICE02 iDoc?

Thank you for your help and best regarsd,

Peter