I need to create a signup page , where user enters his first name , last name and email . these 3 fields need to be sent to a api to check for existing user

Hi @dhruv.gupta

Welcome to the Auth0 Community!

Thank you for posting your question. To achieve the desired results, you will need to combine the Universal Login, which resources you can find here → How to Customize the New Universal Login Page, and use the pre-user-registration action to check for if this exist in the external system Pre-user Registration Trigger

Thanks
Dawid