Hey @Stenr ,
thanks for your question. I’m happy to check on that.
But first: Which devices are you using and are using Multicards as well?
Kind regards, Matea

We are not using multicards. I am on an old Nokia and my son is on a new Samsung Galaxy A13 5G. I have been having this problem for years now and thought it was just my phone, or a particular Finnish number, but now I find out my son has the same problem. If you look back in the feeds, in 2015, somebody is complaining about the same thing, with DNA or Elisa SIM cards in Finland, and there is the back and forth of O2 blaming the Finnish side and the Finnish side blaming O2. https://tuki.dna.fi/org/dna-en/d/receiving-text-messages-from-o2-network-uk/

it seems to be a problem that nobody has resolved. If I am paying for flat-rate all calls and all texts to all European numbers, then this is something you should clear up. Why is O2 being blocked from texting Finnland?

you can also do a search on this

“O2 numbers cannot text finland” and see how common a problem it has been

https://www.google.com/search?client=firefox-b-d&q=O2+numbers+cannot+text+finland

Hello @Stenr ,
thanks for your Feedback. The first Thread you shared is about o2 UK.
Do you get error messages after sending SMS? If yes, what do they say?
Or what does your send status say? Is it a certain finnish provider you can’t send SMS to?
From where are you sending those texts? From home, city center etc. are some SMS going through?
With those questions answered, I will be able to get to the possible reason of  your situation :-)
Kind regards , Matea