For different phone model, the place to do APN setting is different.
Google pixel
Network & Internet => SIMs => Your Line
Make sure the "Mobile data" is ON, and the Preferred Network type is on 4G.
Click "Access Point Names"
Samsung
Connections =>Mobile Networks => Your Line
Make sure the "Mobile data" is ON, and the Preferred Network type is on 4G.
Click "Access Point Names"