Hi @Lunoba, thanks so much for the runbot link, this is quite helpful.
It seems this value has to been an array from the looks of it. Could you try adding a new expression for your field like so:
Then, in the expression editor, enter a value like {{[1]}}:
This will result in an array including a single value of 1. Now the node can be executed without errors:
Fetching the first 5 “Product Templates” would suggest these have been updated as expected:
