"Could not parse mbed app configuration" with MBED OS 6

I am using MBED studio to write an application for the MAX32625PICO to read from and write to an SD card. I gather I need to use SDBlockDevice but when I try to include it, MBED Studio tells me it can’t find it. Some more googling reveals that I need to add a mbed_app.json file to add the “STORAGE” feature and the “SD” component, but when I create an mbed_app.json file with the following contents, MBED Studio tells me [ERROR] Could not parse mbed app configuration from .\mbed_app.json:

    "target_overrides": {
        "*": {
            "target.features_add": ["STORAGE"],
            "target.components_add": ["SD"]

This looks like the same format as all the other mbed_app.json files I’ve seen, but I’ve not found a specification for the required structure. What’s going on here? Am I making a mistake, or is something configured wrong?

It was the trailing comma after "*": {...}