It is essential that Data Roaming is enabled in order to use your eSIM.
1. Open your iPhone settings. Then select the Mobile Data or Cellular Data option.
2. Now tap on the eSIM you want to use, In this section, you can activate and deactivate roaming.
3. Toggle data roaming from disabled as below, to enabled.
4. Enabled data roaming will appear with a green check showing it is on.
Please give a moment for the device to connect to a network. You should then be able to use data roaming services.