The E-Flux app can only be used if you have an account and ordered a charge card via https://dashboard.e-flux.nl/ . With this account details, you can log into the E-Flux app.
Note: are you also using our back office for your charging station? If so, you have already received account details. However, with these account details it is not possible to log into the app. For your own convenience, you could use the same account details so you only have to remember it once.