How to force the notification to turn on from the server not the client?

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    buffer[0] = 13;//24;//13;      // cccd handle
    buffer[1] = 2;       // cccd attribute size = 2
    buffer[2] = 1;//2;       // 1 = enable notifications
    buffer[3] = crc16_compute((uint8_t const*)buffer, 6, NULL);             
        
    err_code = sd_ble_gatts_sys_attr_set(p_ble_evt->evt.gap_evt.conn_handle, (uint8_t*)(buffer), 8, 0);    // initialize cccd attribute
    APP_ERROR_CHECK(err_code);
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    buffer[0] = 13;//24;//13;      // cccd handle
    buffer[1] = 2;       // cccd attribute size = 2
    buffer[2] = 1;//2;       // 1 = enable notifications
	buffer[3] = crc16_compute((uint8_t const*)buffer, 6, NULL);				
		
    err_code = sd_ble_gatts_sys_attr_set(p_ble_evt->evt.gap_evt.conn_handle, (uint8_t*)(buffer), 8, 0);    // initialize cccd attribute
	APP_ERROR_CHECK(err_code);

I add this code in 'static void on_connect(ble_nus_t * p_nus, ble_evt_t const * p_ble_evt) ' on the sever.I got an err_code NRF_ERROR_INVALID_DATA. Softdevice is s132nrf52611. Any suggestions to force the notification?