Recording the reason for a flow failure is very difficult, this is where Power DevBox Exception comes in. It creates a bespoke expression for every flow that returns the reason for why a flow failed.
Instructions
-Goto your flow
-Click save/publish (the exception expression is generated from last full version, not draft)
-Click the Power DevBox Exception Extension icon
-Open the action with the input for the message
-Click paste

Ctrl +e will add expression to return url for flow run -
@{concat('https://make.powerautomate.com/manage/environments/', workflow()?['tags']?['environmentName'], '/flows/', workflow()?['name'], '/runs/', workflow()?['run']['name'])}

Note - expression with skip any scope/container with the word 'exception' in it, this is to stop actions used in exception handling that maybe below the message in the flow (stopping it erroring).
Some actions will not pass errors to containers, these can be individually added. Simply click the icon on the top menu, this opens a popup that adds any action by double clicking them. The expression within the clipboard is automatically updated.