Error authenticating with this Client ID. [Bad Request(redirect_uri_mismatch)]

After running through the set-up wizard following this guide (https://www.cloudways.com/blog/post-smtp-mailer-fork-of-wordpress-postman-smtp-plugin/), I get the error Error authenticating with this Client ID. [Bad Request(redirect_uri_mismatch)]. Flow goes: Grant permission with Google -> Choose Google Account -> Allow Access -> Redirects back to site with this error at the top of the page.

If I deviate from the supplied redirect URI at all, it gives a warning after the Allow Access step still in the Google authentication screen, not on my site.