I'm following a tutrotial and all off a sudden i'm getting this error . I've tried all solution and reinstall module. but in other class the same code work

this is my code

import fileSaver from 'file-saver';



uploadPensiun(event) {

        const files = event.target.files

        const formData = new FormData()

        formData.append('Pensiun', files)

        fetch('http://localhost:5000/uploadpensiun', {

            method: 'POST',

            body: 'Pensiun',

            headers: {

                'Accept': 'application/json',

                'Content-Type': 'multipart/form-data'

            },

        })

        .then(res => res.json())

        .then(data => console.log(data))

        .catch((err) => console.log(err));

        

    }

anyone can help me please?