GitLab Login Error: ERROR for site owner: Invalid domain for site key (reCAPTCHA) ...

Hello Friends:

• Version: gitlab-ce-13.5.4-ce.0.el7.x86_64 (Fedora / CentOS RPM)
• Error: ERROR for site owner: Invalid domain for site key (reCAPTCHA)

I've been running my instance for months and never experienced this error when trying to log into the GitLab UI. As well, I never even setup reCAPTCHA for my GitLab instance (and didn't know this was even possible).

I'm locked out of the UI, even as administrator, because reCAPTCHA indicates an invalid site key (... and therefore no longer renders the expected reCAPTCHA checkbox). A solution would need to be via the Command Line / CLI; e.g. /etc/gitlab/gitlab.rb or gitlab-ctl or something else.

Not that I tried this option (shown here), but it's not being respected:

root# vi /etc/gitlab/gitlab.rb
    nginx['proxy_set_headers'] = { 'X-GitLab-Show-Login-Captcha' => '0' }
root# gitlab-ctl reconfigure
root# gitlab-ctl stop
root# gitlab-ctl start

I have no idea why this started out of nowhere.

Any ideas? I'm stuck. Please help. Thank you in advance!