Upload bulk data as json

I am trying to upload array of Json objects. While I am trying to upload via postman it is showing error in the console as “Cannot set property ‘publishedAt’ of undefined”.
Sample json request:
{

"data": [

    {

        "author_firstname": "authorpostmanersu",

        "author_lastname": "authorerji",

        "author_email": "authorpyuygu@gmail.com",

        "author_mobileno": "9896487699",

    },

    {

        "author_firstname": "authorpostmanersu",

        "author_lastname": "authorerji",

        "author_email": "authorpouyau@gmail.com",

        "author_mobileno": "9896187699",


    }

]

}

for (let i = 0; i < ctx.request.body.data.length; i++) {

    entity = await strapi.service('api::author.author').create(i);

  }