Using the SharePoint HTTP flow action to update a person or group field, I kept getting this error:
A 'PrimitiveValue' node with non-null value was found when trying to read the value of a navigation property; however, a 'StartArray' node, a 'StartObject' node, or a 'PrimitiveValue' node with null value was expected.
The field I was attempting to update is named Submitted By, with an internal name of Submitted_x0020_By. Each time I tried to update the field I was seeing the error noted above. It wasn’t until I looked at one of my previous flow runs did I notice what the issue was. It turns out, that the field name I should be using is Submitted_x0020_ById.