Can’t grant permission with Google

I have run through your nice guide multiple times here:
https://www.cloudways.com/blog/post-smtp-mailer-fork-of-wordpress-postman-smtp-plugin/#step8

Step 19 fails repeatedly for Connection with Google. I click allow using the GSuite account through which the SMTP will send and also the OAuth is created.

I get a 404 error on my site for a non-existent page while the OAuth URL is trying to register
https://URL.org/wp-admin/options-general.php?page=postman&state=**********&code=4/**********=https://mail.google.com/