Problems with OBN target for powerlist

Hi,

I'm trying to extend a powerlist with an additional button. For testing purposes i've copied an existing powerlist and added an invoice button to that.

The powerlist i copied is KYK_CL_SLS_LIST_ALL

I have added his to the get actions method

ls_action-actionid = 'INV'.
ls_action-cardinality = 'S'. "single
ls_action-placement = 'B'. " toolbar
ls_action-enabled = 'X'.
ls_action-placementindx = 3.
ls_action-text = 'Invoice'.
ls_action-add_separator = 'X'.
insert ls_action into table mt_actions.

In the hande_action i have added the following code.
when 'INV'.

clear e_portal_actions.
e_portal_actions-bo_name = 'billing'.
e_portal_actions-bo_op_name = 'Display'.

ls_namevalue-key = 'VBRK_VBELN'.
ls_namevalue-value = 0090000180.

ls_namevalue-key = 'TRTYP'.
ls_namevalue-value = 'A'.

insert ls_namevalue into table e_portal_actions-parameters.

For now i'm just trying to show the above billing document.

In my role i have assigned the transaction VF03 and the following for the OBN target

Method Parameters

billing.display VBRK-VBELN={VBRK_VBELN}

I can't figure out what i am doing wrong. Can someone please guide me?