There are a couple steps listed at the bottom of https://fmod.com/resources/documentation-api?page=content/generated/engine_new_unity/platforms.html#/
Building from Unity
Whenever Unity is started or the platform is changed, the Integration will copy the Banks for the current platform into the Streaming Assets folder.
If you are building from script
BuildPipeline.BuildPlayer()won’t trigger a Bank copy if the target platform is different from the active platform. UseEditorUserBuildSettings.SwitchActiveBuildTarget()to switch to the target platform first.