catching error body using axios post

I had this same issue and the answer (as per Axios >= 0.13) is to specifically check error.response.data:

axios({
    ...
}).then((response) => {
    ....
}).catch((error) => {
    if( error.response ){
        console.log(error.response.data); // => the response payload 
    }
});

See here for more details.