Upgrading from Umbraco 7.15 to 8 (Detected current version 0.0.0)

I am trying to upgrade the underlying Umbraco database from 7.15.8 to 8.

What I have done is spin up a vanilla Umbraco 8, then pointed it to the 7 DB.

The issue is that when I go running the upgrade see the following method

Detected current version 0.0.0 (unknown), which needs to be upgraded to 8.

Once run the upgrade I then get the error

The database failed to upgrade. ERROR: The database configuration failed with the following message: Could not get current version from web.config Umbraco.Core.ConfigurationStatus appSetting.

I have tried setting the value in the web.config, which was blank but it doesn’t make any difference.

<add key="umbracoConfigurationStatus" value="7.15.8" />

This is a companion discussion topic for the original entry at https://our.umbraco.com/forum/109833-upgrading-from-umbraco-715-to-8-detected-current-version-000