Having trouble with key

Hi,

I've created a dataflow where I get and transform an Excel range and push it to the dataverse table.

I'm trying to set a key when mapping the fields before publishing the dataflow.

Firstly, I created a brand new table with a primary column of type text and it populates from Excel to Dataverse fine if I don't set the key but when I run the refresh a second time it adds the same data again resulting in duplicates.

I need to upsert and I understand this requires the key to be set. It seems that it only allows a system key to be selected which expects a GUID argument.

I have a unique column which is of type number in my excel sheet which I want to use for the key but it seems this isn't allowed.

firstly is it possible and secondly how do I implement this?

Thank you so much!

Regards,

Daniel