subsystem request failed on channel 0 when using GCS backend

When trying to connect to you sftp service and you receive an error like

subsystem request failed on channel 0

when using a GCS backend it is likely a permissions issue with your user account on your backend.

The error from GCS that we receive in our logs at this time is: 

failed to connect and get bucket information: googleapi: 
Error 403: username@gcs-ID.iam.gserviceaccount.com does 
not have storage.buckets.get access to bucketname., forbidden

The resolution is to use the permission level storage legacy bucket owner for the user trying to connect in GCS