Please install a "source-code formatter" for Confluence that recognizes C#.
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• Attempted Tag:
  {code:cs|title=ASD.DatabaseLib Usage}

• Error:
  ASD.DatabaseLib Usage

  Unable to find source-code formatter for language: cs. Available languages are: actionscript, ada, applescript, bash, c, c#, c++, cpp, css, erlang, go, groovy, haskell, html, java, javascript, js, json, lua, none, nyan, objc, perl, php, python, r, rainbow, ruby, scala, sh, sql, swift, visualbasic, xml, yaml

• Error Text:

  Unable to find source-code formatter for language: cs. Available languages are: javascript, sql, xhtml, actionscript, none, html, xml, java

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Confluence New Code Macro seems to be a suitable macro plug-in:
https://studio.plugins.atlassian.com/wiki/display/NCODE/Confluence+New+Code+Macro