Problem during update field LIPS-LFIMG in standard table - abap

Question

All the flows seen like okay, however when pass through the call function, the update also failed and the field that need to be update not updated, not sure where is the problem, can someone help me with this problem? do i miss any step?
Error message Log in LT_PROT
DATA: LT_PROT LIKE PROTT OCCURS 10 WITH HEADER LINE.
DATA: LT_VBPOK LIKE VBPOK OCCURS 500 WITH HEADER LINE.
DATA: LS_VBKOK LIKE VBKOK.
DATA: GT_LIPS LIKE LT_LIPS.
DATA: WA_LIPS TYPE LTY_LIPS.
DATA: EF_ERROR_ANY_0 TYPE C,
EF_ERROR_IN_ITEM_DELETION_0 TYPE C,
EF_ERROR_IN_POD_UPDATE_0 TYPE C,
EF_ERROR_IN_INTERFACE_0 TYPE C,
EF_ERROR_IN_GOODS_ISSUE_0 TYPE C,
EF_ERROR_IN_FINAL_CHECK_0 TYPE C.
SELECT * FROM LIPS INTO CORRESPONDING FIELDS OF TABLE LT_LIPS
WHERE VGBEL = LT_BCODE_I-VGBEL
AND VGPOS = LT_BCODE_I-VGPOS.
LOOP AT LT_LIPS INTO WA_LIPS.
WA_LIPS-LFIMG = LT_BCODE_I-MENGE.
MODIFY LT_LIPS FROM WA_LIPS INDEX SY-TABIX.
ENDLOOP.
"VBPOK IS CHANGE INDICATOR, AFTERWARD CALL FUNCTION TO CHANGE FIELD LFIMG IN STANDART TABLE LIPS.
LOOP AT LT_LIPS INTO GT_LIPS.
LT_VBPOK-LFIMG = GT_LIPS-LFIMG.
APPEND LT_VBPOK.
ENDLOOP.
ls_vbkok-vbeln_vl = LT_BCODE_I-REF_DOC.
CALL FUNCTION 'WS_DELIVERY_UPDATE'
EXPORTING
vbkok_wa = ls_vbkok " DELIVERY DOCUMENT NUMBER
synchron = 'X'
no_messages_update = ' '
update_picking = 'X'
commit = 'X'
delivery = LT_BCODE_I-REF_DOC "VARIABLE OF DELIVERY DOCUMENT
nicht_sperren = 'X'
if_error_messages_send_0 = space
IMPORTING
ef_error_any_0 = ef_error_any_0
ef_error_in_item_deletion_0 = ef_error_in_item_deletion_0
ef_error_in_pod_update_0 = ef_error_in_pod_update_0
ef_error_in_interface_0 = ef_error_in_interface_0
ef_error_in_goods_issue_0 = ef_error_in_goods_issue_0
ef_error_in_final_check_0 = ef_error_in_final_check_0
TABLES
vbpok_tab = lt_vbpok "TABLE TO BE CHANGE
prot = lt_prot.

Answer 1

First of all, this function model has the status "Not released" on its attribute tab. That means that it should not be used in customer code, because
SAP might change or delete it in a future update without warning, and then your code won't work anymore.
It is very likely not properly documented.
It might have hidden and unexpected gotchas. Like for example only working for specific corner-cases, not doing everything you would expect it to be doing or requiring to call some other function module before or afterwards in order to do something.
The error handling might be missing or might provide information that's misleading outside of the context where the module is usually used
So before you use a "Not Released" function module, you should check the transaction code BAPI if there is an official bapi function module which does what you want. Bapi function modules are specifically intended for use in customer code. They are well-documented, are guaranteed to take care of everything and SAP promises not to break them in future updates.
So much for the preaching, let's look at your actual problem.
Whenever you encounter a data structure with fields like MSGNO, MSGTY, MSGID and up to four generic variables, you are dealing with a message. You can look up message codes like that in transaction SE91. There we can see that the number 280 in message class VL means:
Required field in interface to delivery update missing VBELN 00000 00000
This could refer to the structure ls_vbkok or to the table lt_vbpok. I would recommend you to set a debugger breakpoint in your code and find out where that VBELN field could be missing a value.