MERN Stack error 500 when sending data to server, how to fix?

Question

Express.js

So I'm creating a store on MERN, the problem is that when registering, an error 500 crashes, the server itself is located on port 5000, I registered the proxy in package.json, but it still doesn't work:

Although when registering a user with an existing email, the server returns a normal response (400) like the user already has one, well, everything is as it should be: