I had been happily using my new Galaxy S21 Ultra 5G smartphone with dual SIM until a software update was installed around 20th July 2021 (Android 11 with One UI 3.1).
After the software update, my mobile internet connection started to drop for a few minutes at random times, then got resumed. This was already annoying, but I tried to find a solution for it and performed a "reset network settings" operation. Shortly after this the error message "SIM 1 not allowed" started to occur and the SIM card that I had been using in the SIM 1 slot did not connect to the network anymore. However, it worked in the SIM 2 slot.
I researched this error message and tried various (possible) solutions:
Should not there be already a solution for this, Samsung? Plenty of users have been complaining about the same issue already for years and various models. It is hard to believe that there so many faulty hardware are built in to SIM 1 slot.
Now I have a brand new smartphone that should be capable of handling 2 SIM cards and I am here with only 1 SIM slot that is functioning for now (the SIM 2 slot). Although the unstable mobile internet connection issue started to occur with it also.
The phone has not been damaged or dropped and I bought it as universal/unlocked as a brand new one in June 2021.
After a sofware update in 2021 July, my mobile internet connection became unstable and temporarily terminated at random times. Shortly after resetting the network settings in hopes of fixing the issue, the phone started to display the error message "SIM 1 not allowed" and the SIM 1 slot has not been functioning ever since.
Please provide a solution for the issue if anyone had luck to resolve the "SIM 1 not allowed" error on S21.
Yes, the phone was purchased as brand new. The SIM 1 slot hosted the SIM card that started to encounter the unstable mobile internet connection issue after being in use for 1.5 month. (Now it is in SIM 2 slot.)
None of the SIM cards can connect to the network in SIM 1 slot now.
Hello @Krisztina K
If this was my phone then I would ask the original supplier of the phone for assistance and or approach a Samsung Experience Store or Samsung Service Centre for them to take a look at what is going on with your phone.
Current Phone > Samsung Z Fold³ 5G.
Update: the root cause of the error message "SIM 1 not allowed" was found.
I was told in a Samsung Service Centre that the phone's IMEI is blacklisted. I used the "Blacklist Pro" (paid) service of https://www.imei.info/phone_blacklist_check/ webpage that revealed which carrier has blacklisted my phone's IMEI. So I contacted the carrier's customer service and they told me that the phone's owner has not paid installments and as these are overdue, they blocked the IMEI.
As I bought the phone as "new", I already claimed a refund from the seller as obviously I am not the original owner of the phone, but someone else.
Nevertheless, I'd suggest that Samsung rephrases this error message "SIM 1 not allowed" in a way that clearly tells that the issue is with the phone's IMEI as I wasted plenty of time until the real cause of the error got revealed.
Thanks for your replies!