In some cases, Octopus are missing half hourly data from one of your meters, which means that my website can't retrieve it via the api. It is worth taking a look on the Octopus website itself - if you can't see the half hourly data there, email Octopus and ask them if they can try and get that working. Once you can get the half hourly data from Octopus, my website should be able to pull it in.