Cellular Data not working on iPhone 8 plus

I ASSUME YOUR CARRIER IS NOT SPRINT OR A SPRINT MVNO--IF IT IS YOU CANNOT HOT SWAP SIMS.

You said that you checked for carrier updates--do you mean ##UPDATE#?

If you have not done a carrier reset (##CLEAR#) try that and then ##UPDATE#.

The next thing to check is your APN settings.

View and edit your Access Point Name (APN) on your iPhone and iPad - Apple Support

If you APN settings are correct, you might view the outage map for your carrier to see if there any issue in your area.

If you can't connect to a cellular network or cellular data - Apple Support

My new iphone8 plus constantly constantly constantly searching even though I’m connected and everything else working fine!? Why why why!! let me know what you find out!

I have a fetching problem on my iPhone cellular data(Mobile Data) not working. Because I moved to another network before a week. I found an online guide about the cellular data not working and it worked for me.

Source: https://www.howtoisolve.com/fix-iphone-cellular-data-not-working/

mmabli wrote:

I still have the sim card from my old iPhone 6s, and I'd rather try everything before restoring...

It's not clear what this means ... are you using a SIM card from your iPhone 6S currently? (I don't even know if it would fit in a iPhone 8 plus).

Anyway, regardless of the above, what did your cellular carrier tell you when you contacted them? And presumably your voice connection works just fine.