Bad request when submitting extension

The error was a comma at the end of entitlements

    "entitlements": {
        "process": true,
    },

the extension ran and installed fine during development.

I had to remove the comma to get it to submit.

    "entitlements": {
        "process": true
    },

This is due to a difference in JSON parsers. Swift’s JSON parser accepts trailing commas, as it supports JSON5 and other variants. Python, which we use on server, does not support trailing commas.