To add to btbam91's reply: responseType has to be part of the config. In the above example:
axios .post('http://0.0.0.0:8000/sheets/', data, { responseType: 'arraybuffer', headers: { 'Content-Type': 'multipart/form-data', } })
The problem was that 'responseType': 'arraybuffer' should not be in "headers."