We have a use case where we have one board with a list of assets on it, and we use the Unique ID column to assign a number automatically to that item.
When the item is sold, we create a duplicate item in another board and copy over some of the detail - this was relatively easy to set up and works well. however, I can’t copy of the Unique ID number.
For the recipe you use when the item is sold - swap with this below recipe to create your item in the other board but also connect the two boards together with a connected board column.
Once you have the connected board column in place, you can mirror the Unique ID instead of trying to map it across. Give it a try: