@Paytonsopa
The most common issue is that the wireless password that is being typed into Kasa is the incorrect one. To verify that the wireless password being used is correct, I would recommend going into your phones settings, then WiFi. Forget the wireless network that you are trying to connect the smart device to, and then reconnect. When the phone asks for the wireless password, use the same password that you tried in Kasa.
One other thing to look for is when you are at the screen where you join the device to the network. The wireless network name should be the one you normally connect to to give internet, if not, select the link below to choose a different network name.