I was adding my connection string, and I initially specified an SQL account that was disabled accidentally. I then amended the string to use an active account, but the installer then would not progress and continued to prompt me “Error connecting to the databse. Login failed for user ‘username’. Reason: The account is disabled”.
I then closed the configuration screen and located it again via the Octopus > Server Tools start menu item, and it accepted my new connection string without a problem.
Only a small bug 