TLDR 

Updating a couple of field types in SharePoint Online isn’t quite so easy
We wanted to share a quick walk-through of how to update a couple of field types when using Microsoft Flow to update a SharePoint item or file properties.

Two field types require you to use a more advanced action in Microsoft Flow…Hyperlink and Image columns.

Instead of using the standard “update item” action in Microsoft Flow, you have to use the “Send HTTP Request To SharePoint” action. This requires you to write some JSON to update your items.