The APN (Access Point Name) tells your phone how to reach the internet on a network. Most phones set it automatically. Sometimes they don't, and you get bars but no data.
Find your APN
Open My eSIMs → your eSIM → Install steps (or Install & codes). If your plan needs a specific APN, it's written there.
iPhone
Settings → Mobile Service → kimsim → Mobile Data Network → type the APN in the APN field under Mobile Data. Leave username and password empty.
Pixel and most Android
Settings → Network & internet → SIMs → kimsim → Access Point Names → + → Name: kimsim, APN: the one from My eSIMs → Save, then select it.
Samsung
Settings → Connections → Mobile networks → Access Point Names → Add → fill in as above → Save, then select it.
Then restart the phone. Still no data? Talk to a human.