Snippet from https://betterprogramming.pub/upload-files-to-next-js-with-api-routes-839ce9f28430

upload.axios.ts

...
const config = {
  headers: { 'content-type': 'multipart/form-data' },
  onUploadProgress: (event) => {
    console.log(`Current progress:`, Math.round((event.loaded * 100) / event.total));
  },
};

const response = await axios.post('/api/uploads', formData, config);
...