OpenGameArt.org
Forest on Rails - 8-Bit Chiptune Stage Music
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"Forest on Rails - 8-Bit Chiptune Stage Music" by Volcano of Bears licensed CC-BY 4.0: https://opengameart.org/content/forest-on-rails-8-bit-chiptune-stage-music
Where to put it: Game credits or video description. If the entry has a "Copyright/Attribution Notice", follow that.