I think for the PodPoint ones it’s the PodPoint app & it takes £10 the first time you use it, which then stays there if you only use their free chargers.
Not sure how the Polar works as I have a PolarPlus card (3 months free when you open the account, then added 6 months free via the referal code that Peugeot sent me for the car, after that it’s £7.65 a month I think so wouldn’t be worth having but there is a Polar App too with different rates).