OK so I have been using my Samsung a13 4G without any issues for the past 4 months. This morning I got a notification saying sim one not allowed. The notification quickly disappeared but ten minutes later it happened again twice. I just happened again now. It seems to be when I have low service. My sim is in sim card one. I have installed the android 13 update and I seem to still be able to use the sim while the alert is there. Has this happened to anyone else?
I haven't had this on my phone which I use two physical sims inside @Soph1234
You could try as a first stepping stone this > Clear Cache Files from the phone's System Partition Section > https://www.samsung.com/uk/support/mobile-devices/how-do-i-clear-the-cache-on-my-device/ You may need to insert your earphones or hook upto a powered On Laptop to access the Clear Partition Section. This may help with lag or stutters as this clears the phone of old/unused or broken cache files.There is also a Repair Apps option in the Menu System too.