By default, mobile data on the LG smartphone can only be used in your own "home" network, but if we are in another network, or even abroad, data roaming must be activated so that the Internet can be used on the LG device.

Android 9 | LG UX 9.0
Data roaming -  Open the  Settings
Data roaming -  Tap on  Mobile networks
Data roaming -  Tap on  Data roaming
Data roaming -  Choose between  Off ,  National only  and  All networks
  1. Open the Settings
  2. Tap on Mobile networks
  3. Tap on Data roaming
  4. Choose between OffNational only and All networks

LG Instructions