Unable to Activate an update is required to activate your iphone

i have an iphone 7 plus i wasnt using it for about a year now when i turn it on its telling me unable to activate an update is required to activate your iphone i plugged it to my pc and used itunes to update it it download the file of 5.39gb for version 15 and updated successfully when the started back up its telling me the same thing unable to activate an update is required to activate your iphone.

Can anyone help me