ASP.NET Inserting data into entity with Azure SQL Database

I am new to ASP.NET if someone could explain why this doesn't work or how to set it up correctly would be great

This code:

    [HttpPost]
    public string Post([FromBody] User account)
    {
        Accounts newAccount = new Accounts { FirstName = account.FirstName, LastName = account.LastName, 
            Email = account.Email, Username = account.Username, Password = account.Password };

        using (AccountsDbEntities entities = new AccountsDbEntities())
        {
            entities.Account.Add(newAccount);
            entities.SaveChanges();
        }

        return "Success";
    }

Is returning this error:

System.ArgumentException: 'The ADO.NET provider with invariant name 'System.Data.SqlClient' is either not registered in the machine or application config file, or could not be loaded. See the inner exception for details.'

For this line: entities.Account.Add(newAccount);

I am using ASP.NET Core 2.1 with ADO.NET Entity

Is my code wrong or is it configuration?