What Causes iPhone's "Last Line No Longer Available" Error?
The 'Last Line No Longer Available' error has existed on the Apple iPhone since iOS 12; it is not new. iPhone XR, iPhone XS, iPhone XS Max, iPhone 11, 11 Pro, 11 Pro Max, iPhone 12, 12 mini, 12 Pro, 12 Pro Max, iPhone 13, 13 mini, 13 Pro, and 13 Pro Max were affected by the issue.

When a user attempts to make a call from the default line through the phone app's recent logs, the error message "last line no longer available." appears on the screen. Do you wish to use your remaining phone line?"

For those unaware, iOS allows you to set the default line (phone number) that iMessage and FaceTime use when the device has two active SIM cards. In addition, the iPhone allows you to use the default line when calling or texting individuals who are not in your Contacts app. Depending on your needs, you have the option of setting your default line for calls and messages and using the other line exclusively for cellular data.

Users are unable to dial a contact using their preferred SIM card due to the error. Therefore, they must utilize the remaining line for this purpose. Well, we will demonstrate how to resolve the 'Last Line No Longer Available' error on your newly purchased iPhone 13.
https://wikiguide.tips/how-to-fix-last-line-no-longer-available-on-iphone