Function pa_context_send_message_to_object 

pub unsafe extern "C" fn pa_context_send_message_to_object(
    c: *mut pa_context,
    recipient_name: *const c_char,
    message: *const c_char,
    message_parameters: *const c_char,
    cb: pa_context_string_cb_t,
    userdata: *mut c_void,
) -> *mut pa_operation

Available on crate feature pa_v15 only.