Delete name data from managed column using "Send an http request"

Hi 

I'm trying to use Power Automate to reset an approval process and delete the name populated in the "Rejection" column from a previous approval flow. I have followed the instructions at How to clear fields in SharePoint list items using Power Automate (sharepains.com)

However I am getting an error "The property 'RejectionStringID' does not exist on type 'SP.Data.Shared_x0020_DocumentsItem'. Make sure to only use property names that are defined by the type."

I have checked the internal name for the Rejection column by going to "Edit Columm" and looking at the site address which confirmed Field=Rejection

I would really appreciate some help!

Step in flow:

SharePoint site