Make sure you have the correct area code and entered the correct site number.
If you have location services activated on your mobile phone, an area code nearby may sometimes appear. Make sure you have the correct area code in the app for the area you parked in.
If it is a public car park, there should be signs telling you which code applies. Otherwise, you can always scan the QR code on the socket. This will always bring up the correct area code and location number.