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
Step 1:  Open the  Settings
Step 2:  Tap on  Mobile networks
Step 3:  Tap on  Data roaming
Step 4:  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