SS Khan,
there are couple notes regarding this issue. Note 1308330 - WebUI: Account search gives no result and subsequent Note 1462146 - BP_HEAD_SEARCH/SearchHelp shows incorrect configuration.
They only fix the issue when you delete some category (for instance category 'Group') and keep 'All Accounts' option in dropdown list in place.
What you need is different. As I understood you need to keep only one category and even skip 'All Accounts' option. If so the correct flow will be:
1. Do as you're doing in GET_V_CATEGORY method. This will restrict the dropdown list.
2. You need to default category value in shuffler other than empty (which relates to 'All Customers' option).
For the second step proceed as following:
1. Enhance the BP_HEAD_SEARCH/CuCoShuffler custom controller.
2. Redefine its method DO_INIT_CONTEXT.
3. Place the below code there:
METHOD do_init_context. DATA: lr_node TYPE REF TO if_bol_bo_property_access. lr_node ?= me->typed_context->search->collection_wrapper->get_current( ). lr_node->set_property( iv_attr_name = 'CATEGORY' iv_value = '2' ). "Accounts ENDMETHOD.
Hope this will help you.