On top of hsujdik comments you can use SendRequestAlt function, it is very similar but accept input (event atteributes) as list and user data can be set all at once (either as json string or kvlist already created) something like
LIST list = KVListInit[‘thisdn’, v_thisdn, ‘connid’, v_connid, ‘{l}userdata’, ‘{“abc”:123,“cde”:“tyu”}’]
SendRequestAlt[RequestUpdateUserData,list]
or
LIST v_userdata = KVListInit[‘abc’, 123, ‘cde’, ‘tyu’]
LIST list= KVListAddList[ KVListInit[‘thisdn’, v_thisdn, ‘connid’, v_connid’], ‘userdata’, v_userdata]
SendRequestAlt[RequestUpdateUserData, list]