@Mikayo can you make Voice calls to land line or mobile numbers? Did you have mobile signal? If this a complete new mobile contract?

@Joe Doe Yes I can make voice calls to landline and mobile numbers. But I just can’t send any SMS or text messages. 

I think it is a new complete mobile contract. Or how can I verify this?

@Mikayodid you use multicards for your contract? 
edited: Can you receive SMS with your IPhone?

@Joe Doe Yes I have multi cards. Two nano sims. One for the phone and one that I was told by the O2 store to use on a Tablet. 

Yes I have already received SMS on it. 

Thank you for the response. 

@Mikayo ok. You can receive SMS with your IPhone, but you can’t send any SMS. Can you deal *#5005*7672#  What is the answer.

edited: code not work with iOS 13.3

@Joe Doe 

Yes I can receive SMS but I can’t send any. 

I just dialed the code. It says “Error performing request Uknown Error”

@Mikayo Settings/Messages “send as sms” is activated?

@Joe Doe I just activated “Send as sms! Still doesn’t work. 

@Joe Doe I think it now works . I just had to switch off and on again. Thank you very much!!

@Mikayo stupid question. Have you try to send in international format? Like +49 179 XXXXXXX? 
In the Moment I run out of options. Multicards can send all SMS. Receive only one multicard at the same time. But receive is not your problem.

edited: nice . Stay healthy in these days.

Leider gibt es zu einem Anliegen 2 Topics. Hier schliesse ich, dort geht es weiter https://hilfe.o2online.de/english-o2-community-mobile-43/sms-not-working-on-new-sim-card-527645#post2057372