Thanks, @blackview_admin and @MRUK. My carrier suggested I root the device and follow a series of commands using a cable connected to the PC. I'm not interested in rooting a device belonging to my customer. I understand this is indeed an issue with Android 8.1 - hence my question about if 8.0 is ava...

I have three BV5800 devices. They came with Android 8.1. I need to change the APN settings to make them work with our carrier's network. But the APN settings only show pre-configured options and there is no "Add" nor "+" button. If I long press on an existing APN configuration th...