Are you trying to restore backup from another CHR? Are you trying to license a CHR that was used for free longer than 60 days?
For me I had built the CHR in Proxmox using the raw image converted to qcow (as per MikroTik's documentation). I had it check out a license (which was free, because it was new). Once I was happy with how it was configured and working on the first host, I migrated and/or cloned it to the second host. When I went to licensing to generate a new license for the cloned VM, it gave the error. Even after changing the system ID (so I could get a new license), it gave the error.
My workflow is to spin up the VM, ensure it's working correctly, then clone it to all the other hosts. This has worked fine on VMware in the past, so I don't know what extra step(s) I may have done in Proxmox to cause it to complain. I would happily buy licenses for them, but in this particular scenario, it wouldn't even check in so I could assign a paid license to the newly generated system-ID.