Trying to access API via CURL

I bought a new Water Softener, model Ypsilon 6G BWT. It’s a Chinese-made, European distributed device, quite nice. It has WiFi connection, controlled via their own Water Device app:

I’m trying to access their API to get data into HA, but I’m stuck. I know the app communicates with this site:

api.waterdevice.net

Any help or tips about how to access the site via curl with my credentials? Thanks!