Character in front of every API request

Hello, while developing API, I noticed that every request has character "x" in front of it. I cant find anything that might cause it. Did I mistakenly added x somewhere and where it might be added, as of it appears on every request.

x{
    "data": {
        "id": 1,
        "category": "Pizza",
        "author": "Lonzo Pfannerstill",
        "author_id": 9,
        "title": "Non quo nostrum labore dolor eos.",
        "content": "Consequuntur qui molestiae molestias eum.",
    }
}