SharePoint - Set value of Related Items column

Hi everyone. I'm trying to create a SharePoint Task List Item using Power Automate. I'm using SharePoint-Create Item action to create the item. Once created, I have another SharePoint-Send HTTP Request to update the item and set the value of Related Items. The Power Automate runs successfully but the Related Item field is not being updated. It's value (from view) is empty and I am expecting the value to have '1 related item'. 

Screenshots below.

Any help is appreciated. Thank you.