I'm trying to upload a json file using TS and the firebase admin module

async function uploadFileV2(filename, path) {
    await bucket.upload(path, {
        destination: `json/${filename}`,
        metadata: {
            contentType: "application/json"
        },
    });
}
uploadFileV2('test.json', 'C:/path/to/json/file')

Once the file is uploaded it appears in the storage bucket as undefined but with the choosen name. I tried it with uploading a png and using the contentType: 'image/png' and it worked fine. (Uploading a json file manual does work, too) What am I doing wrong? Thank you for your help!