Signal says SOS - HOW DO YOU FIX THIS?

I have Verizon.

I was unable to make phone calls or receive any text. I tried the hard reset— didn’t work. I tried resetting NETWORK SETTINGS on iPhone— didn’t work.

it was saying, “SIM FAILURE” whenever I reset phone.

What I decided to do was, get a paper clip and push my SIM out. Waited a minute and carefully inserted it again. Then I did a hard reset by pressing VOLUME UP, DOWN then HOLD DOWN POWER BUTTON until it shows SLIDE TO TURN OFF. SLIDE IT AND TURN IT OFF. Wait 1 minute and turn it back on.

I immediately started receiving texts I didn’t receive and voicemails that didn’t go through.

I hope this helps and works for you too!