Good Day 

Please note the fix you mention above is not related to the article Known Issue: K2 5.6 upgrade failing on the configuration service. | Community (nintex.com). The article still needs to be followed if the issue occurs during installation. 

I'm careful about this too, and I like to test things ahead of time because I don't trust that everything will go smoothly. According to my know-how notes, I encountered this issue, related to the use of client SQL alias, back in September 2022, during my internal testing of the upgrade process, shortly after the release of K2 Five 5.6, the installer version was 5.0007.1000.0. I was able to get out of this bad situation, where the K2 Configuration Server service was not starting, by decoding the encoded SourceCode.Configuration.Api.dll.config file, where I changed the SQL alias in the connection string to the actual SQL Server name.
I then note in my notes that this was resolved with the installation package "K2 Five (5.6) (5.0007.1000.1)". And also a note - don't use older versions of the installers. 
I would strongly recommend making a good backup of the entire K2 environment (VM and SQL DB) before upgrading, so that the original working state of the environment is captured and can be easily reverted to if problems arise.
Fingers crossed with the upgrade, in the worst case scenario there is Nintex Support that can help you get out of the problem, but sometimes it may not be as fast as you would need. But it's all about money, e.g. the level of support you pay for.

Hi @tobrien_stewart 
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