You need to wait a few minutes after you spawn the structure for the tool to recognize the owner, then remove the core and replace it, wait again, and finally use the command.
If you don’t wait long enough with the normal core then it can’t determine the owner.
“You want to place it in your structure and get the ID of that structure BEFORE placing / replacing the core. Also make sure this structure is not new created. Otherwise wait at least 2 minutes before you proceed.”
An admin may be able to help you. Next time just wait longer before removing the core.