It looks like you're attempting to upload a file to the pinJSONToIPFS endpoint, which is intended to purely be used for JSON that is passed in via a request body.

In your situation I would recommend using Pinata's pinFileToIPFS endpoint

Here's some example code based on their documentation that may be of help:

//imports needed for this function
const axios = require('axios');
const fs = require('fs');
const FormData = require('form-data');

export const pinFileToIPFS = (pinataApiKey, pinataSecretApiKey) => {
    const url = `https://api.pinata.cloud/pinning/pinFileToIPFS`;

    //we gather a local file for this example, but any valid readStream source will work here.
    let data = new FormData();
    data.append('file', fs.createReadStream('./yourfile.png'));

    return axios.post(url,
        data,
        {
            maxContentLength: 'Infinity', //this is needed to prevent axios from erroring out with large files
            headers: {
                'Content-Type': `multipart/form-data; boundary=${data._boundary}`,
                'pinata_api_key': pinataApiKey,
                'pinata_secret_api_key': pinataSecretApiKey
            }
        }
    ).then(function (response) {
        //handle response here
    }).catch(function (error) {
        //handle error here
    });
};