The key may not have been loaded into the SmartFill GEN2 unit or may be an incompatible type key (not a genuine manufacturer supplied SmartFill GEN2 unit key). You can add via the admin menu at the unit or by adding them at the website.
If the front of the SmartFill GEN2 unit is wet, you may need to dry the area around the key sensors with a tissue or clean rag. Moisture around the sensors will cause the keys to misread.