Khun Jaruwan/MOD called to front desk and inform room 528 guest at the balcony they can’t open the door go back in room, GSA copy the key card go to guest room for open the door but can’t open it show red/green light, After that called to ENG to check and changed to battery but still not open and Onity machine can’t be opened, After we take so long times (around 20 min) DM use emergency key card(from F/O) to open the door and immediately open the balcony door from inside, Finally DM apologize to guest for inconvenient and inform ENG team for check the balcony door again, Guest was fine and thank for our action.