We upgraded to TeamCity 9.1 yesterday and started getting the following build error:
symbols.sources-server-url configuration parameter was not set. No symbol and source indexing will be performed.
So, I downloaded and installed the current Symbol Server plugin https://confluence.jetbrains.com/display/TW/Symbol+Server
It does show up in the list of plugins as version 1.0.6, but when I go to Build Features to add the Symbol Files Indexer, it doesn't show up in the list of available build features. Is there something else I need to do?