If you see the above error on shipments when trying to create an InPost label, it means that Shiptheory found a locker ID in your order data however InPost rejected the order because it does not recognise the locker.
Please check that the locker ID on your order is correct. You can search for valid lockers on the InPost website here. You can check the locker ID by clicking the location marker on the map. The locker id is in the title and starts "UK...". As shown in the screenshot below: