In order to use EOIO (Exactly-Once-In-Order), you have to pass the Queue ID to the class before calling the Outbound Proxy in your ABAP Program. It can be a static value like shown below (parameter) or a dynamic object like a document number:
PARAMETERS: p_queue TYPE sxmsqidapp.
DATA: l_proxy TYPE REF TO z…,
async_messaging TYPE REF TO if_wsprotocol_async_messaging.
CREATE OBJECT l_proxy.
async_messaging ?= l_proxy->get_protocol( if_wsprotocol=>async_messaging ).
async_messaging->set_serialization_context( p_queue ).
