Not meaning to resurrect a dormant post, but I thought I'd post to offer help to anyone else who encounters this.
I had this same issue and it was caused by me having extra license keys in my /boot/config folder.
-rw------- 1 root root 256 Nov 15 2021 Basic.key
-rw------- 1 root root 256 Jul 9 2023 Plus.key
-rw------- 1 root root 256 Oct 4 2021 Trial.key
I removed all but Plus.key and then then I was able to replace the key. I also used the latest Unraid Connect plugin to help with this. It pointed out the multiple key files.