How to activate a sim card with this error: "The SIM card for the ICCID you entered is already in use and cannot be activated again"
I have an old iPhone 8 that I want to add for a second line. The 8 was my own phone purchased from and used on my AT&T account. When I go to add a new line by checking the sim card, the AT&T tool recognizes the IMEI but not the ICCID. It gives the error, "ICCID not found". WHen I go to the AT&T "Device information" page, the ICCID info gives me this error: "The SIM card for the ICCID you entered is already in use and cannot be activated again. If your device is not working properly with this SIM card, please order a new SIM card before you activate your device." Any advice for next steps?