Was your phone originally on Android 8.1 and then upgraded to 9? Here's a link involving APN problems with an Umidigi 3 https://productioncommunity.publicmobile.ca/t5/Getting-Started/android-8-1-apn-settings/td-p/357072
What is your phone? I've just checked my SIM with Redmi Note 8 and Galaxy J1. They both create and connect to hotspots easily and internet is working for a connected device.
It's a Umidigi A5 Pro.
@hycm53 wrote: There is a small app can add new APN on Android phone. I used it for my Asus Zonfone 4 Max to add new APN. If you need it send message to me.
Another suggesting is turn off data saver on your phone.
Is the app the one from RFD? "MyNewAPN"? I installed this, removed the sim card and restarted and it still doesn't work. Maybe it's specific to my phone?
Unfortunately, data saver is off already.
If the app is different, I'd be happy to try it as well
Yes, It's called "MyNewAPN_test". I think it's the same as you said.