email-exists | Check whether an email address exists | Email library

In my Angular 6 app I have async validator for checking if typed email is already registered but right now I'm getting 'Expected validator to return Promise or Observable' and I don't really know why.

I would like to change the WooCommerce registration error message that appears if an email address is already registered.

To make it safe for updates I execute this code (not working code) in my child functions.php

This is the html for my page

I'm having some issue with a register form I've been trying to code. The error I get is a 404 error saying that a referring link is outdated or incorrect.

I'm confused as to why, as I know the file exists within the same directory and I have called it as such.

Please see the below. If that isn't enough, I have linked the whole project here

As far as I can tell, the error seems to be coming from a referring link with in my check-registration.php which is the action to which my form post points:

Checking registration php:

I am trying to allow users to edit their email address in my PHP system but also prevent them from setting one that already exist, I am also trying run them through FILTER_VALIDATE_EMAIL. However it stops somewhere for me. The checks works fine in same function, but updating the the new one if the checks that I tried to setup are passed doesn't work. I am using a HTML form for updating them. I thought I did it right, I read here check if email exists in MySQL database that it should be possible to do it this way.

Here's my code, does anyone see what I am doing wrong? Where am I missing out?