O2 UK (Pay As You Go ) APN Mobile Data and MMS Internet Settings in 2 min on any Android Device

https://www.apnsettings.org/uk/o2-apn...

I don't have O2 phone, neither I have O2 Sim that's why after saving APN, I didn't get that APN option, but if you do have O2 phone with O2 sim you should see APN , check that APN listed there, restart the phone and you should have Data and MMS working.