Today many people face this error.
To solve this first you log in to mongodb. Then select the Database Access option from the sidebar.
Next, from there click on the Edit button next to the user you were using. I think the username is dbUser2.
After that, if you scroll down to the modal that appears, you will get the option to write “built-in role”.
Click on this accordion item/option and click the “Add Built in Role” button, then the “Select Role” dropdown. From there select “Atlas Admin” or “Read and write to any database”. Then update by clicking the “Update User” button at the bottom. Then restart server side terminal and run nodemon index.js command.
Hope it gets resolved. If not contact our support session.