Hi,
I am trying to automatically populate default lookup ID in edit form data card, the card has a combo box field. The underlying sharepoint lists are "Transactions" and "Transaction Log". This edit form is about adding record to "Transaction Log" when user select Add_Note button of an item of gallery "Transaction".
"Transaction Log" list has a lookup column "Transaction ID" which is linked to the default ID column of "Transaction".

When this edit form shows up, I want the data card "Transaction ID" automatically populated with the transaction ID selected in the transaction gallery, so I set the combo box's defaultSelectedItems field to below, but got error shown.

First of all, is this the correct field to set the default choice in combo box card? Second, what is the right formula and what does the error mean?
Thanks