Store vars in a separate file

[MelaAxel]

I have need to point different runs to different TestRail projects, so I need to specify that config at execution. That works fine by using the proper flags for the Cy run. However, for security, I don't want my TestRail creds stored in those env.json files; additionally, to limit the duplication of files in my setup, I want to use a 'testrail.json' file to store all the config settings that I will reference for that run.

Dumbing this down to a single file / config, I've moved the 'testrail' section of the env.json into a testrail.json file and tried using a $ref:

but I get this error:

What am I missing to get this working correctly while storing these variables in a referenced file?