In the end of 2020, SendGrid Officially noticed to all of its customer to switch from basic authnication (username and passowrd) to API Key based authenication named as V3.
In this code sample you will find a working solution if your site running with ASP.NET MVC 4.0-4.8 with C#. Don't know the suppport for VB.NET. You need to write this code in a seprate class or in a Library Project for the sake of SOC. Also need to pass your API key either from envoirment variables, appsetting or from DB (Secure your API Key Always). Rule: recoemend ways is that not to store key in source code ever!). The SendGrid Email Client for sending the email with API key. An advance API Key based authentication by SendBird.
Stay Safe and Enjoy Coding!