Help on understanding on making a JSON patch from another mod

[MAZ12211]

How do I add {"id": "mania", "x", -2} in the difficulties array from another mod?

{
    "difficulties": [
        {"id": "insane", "x": -10, "y": -5},
        {"id": "duet", "x": -9},
        {"id": "chill", "x": -10, "y": -1},
        {"id": "edit", "x": -2},
        {"id": "4k", "y": -2},
        {"id": "7k"}
    ]
}

I tried doing [{ "op": "add", "path": "/difficulties/-", "value": "{"id": "mania", "x": -2} }] but it didn't work

[MAZ12211]

Solved! It was a syntax error [{"op": "add", "path": "/difficulties/-", "value": {"id": "mania", "x": -10}}]