Axios发布和上传图像无法在IOS / IPhone上的Safari（HTTP 400）上运行

Question

I have a website in which users can upload their profile image through a Vue.js component using Axios

All works perfectly with Chrome or FireFox but on Safari the post request return code 400

Which could be the problem?

Here is the code of the Vue component:

persist(file){

        let data = new FormData();
        data.append('avatar', file);
        axios.post('/api/users/'+ this.user.id +'/avatar', data)
          .then(() => flash('Profile image updated!', 'Your profile image has been saved successfully'));
    }

And this is the only log i have from Google App Engine:

2019-08-08 12:20:21.994 CEST POST 400 0B 24,4s Safari 12 /api/users/5/avatar

Thank you