Comment by dimfeld

I have no inside info, but it sounds like the key was inadvertently bundled into the client-side code. This could happen when using web frameworks that do both client-side and server-side rendering, if one of your client-side files imports something from a file that is supposed to be server-only, and contains the API key environment variable.

Some frameworks automatically detect this and fail to build if you do it, but apparently not all of them.