Here are some possible ways to fix the “SIM not supported” issue on your iPhone 13 Pro Max:
* Check for carrier settings: Open ***Settings*** > ***General*** > ***About*** > ***Carrier Lock***. If your iPhone is locked, contact your wireless carrier about unlocking your iPhone. If you don’t see this option, or if it says something else, try the following methods.
* Eject and reinsert the SIM card: Look for the SIM card tray on the side of your iPhone. Use a SIM card ejector tool or a straightened out paperclip to open the tray. Push the tray back in to reseat the SIM card.
* Force restart your iPhone: Press and quickly release the ***Volume Up*** button. Press and quickly release the ***Volume Down*** button. Then, press and hold the ***Side*** button until you see the Apple logo.
* Reset network settings: Open ***Settings*** > ***General*** > ***Transfer Or Reset iPhone*** > ***Reset*** > ***Reset Network Settings***. Enter your iPhone passcode, then tap Reset Network Settings to confirm your decision.
* Update iOS with Reiboot: You can use Reiboot to update iOS on your iPhone 13 Pro Max. Download and install Reiboot on your computer. Connect your iPhone to your computer with a USB cable. Click on “Repair Operating System” and then “Fix Now”. [link|https://www.youtube.com/watch?v=jlVfpDi2IoY|Follow the instructions on the screen to download and install the latest version of iOS|new_window=true]