railpack.json startCommand not recognized

Question

We're in the process of migrating from Nixpack to Railpack and running into the issue where the `startCommand` in the `deploy` property is not being recognized by Railway. See the config and error below.

Gotten from the docs here: https://railpack.com/config/file
```
{
    "$schema": "https://schema.railpack.com",
    "steps": {
        "install": {
            "commands": [
                "pnpm install"
            ]
        },
        "build": {
            "inputs": [
                {
                    "step": "install"
                }
            ],
            "commands": [
                "moon backoffice-api:build"
            ]
        }
    },
    "deploy": {
        "startCommand": "moon backoffice-api:start"
    }
}
```

``` ✖ No start command detected. Specify a start command: https://railpack.com/config/file```