Bad request codigo 400

hola soy nuevo en sitio y tengo este problema al insertar en la bd estoy usuando laravel5.8

el siguente problema es que me arroja un error 400 bad request y uno del QueryException con el SQLSTATE[23000]: Integrity constraint violation ` registrar(){

			const data = {

				'name': this.datos.name,
			 	'usuario': this.datos.usuario,
			 	'email': this.datos.email,
			 	'localidad': this.datos.localidad,
			 	'descripcion': this.datos.descripcion,
			 	'password': this.datos.password,
			 	'password2': this.datos.password2,
			 	'rol_id': this.datos.rol

			};

		axios.post('http://127.0.0.1:8000/api/user', data)
			 .then((response) => {
   			 console.log(response.data);
				  })
			  .catch((error) => {
  				  if (error.response) {
         				 // The request was made and the server responded with a status code
          				// that falls out of the range of 2xx
         		 		 console.log(error.response.data);
         				 console.log(error.response.status);
         				 console.log(error.response.headers);

       			 } else if (error.request) {
          				// The request was made but no response was received
          				// `error.request` is an instance of XMLHttpRequest in the browser and an instance of
          				// http.ClientRequest in node.js
          				console.log(error.request);
       			 } else {
          				// Something happened in setting up the request that triggered an Error
         		 		console.log('Error', error.message);
        		 }
			 })

		}`