what to do to fix this?
Thank you!

sudo -u git bin/check
Check GitLab API access: FAILED. code: 404
A simple search - https://github.com/gitlabhq/gitlab-shell/issues/37 reveals that URL set in config.yml for gitlab-shell is incorrect and causes 404 error.
config.yml. I'd given Gitlab a custom port on nginx, but forgotten to set this in the URL field. In my case, http://localhost:8234/ solved the issue.If you still get 404, review the vhost config. Next you can find an example from a Mac OS X apache machine:
<VirtualHost *:443>
ServerName domain.com
DocumentRoot "/Users/git/gitlab/public"
CustomLog /var/log/apache2/access_log combinedvhost
ErrorLog /var/log/apache2/error_log
<IfModule mod_ssl.c>
SSLEngine On
SSLProxyEngine On
SSLCertificateFile "/etc/certificates/domain.com.cert.pem"
SSLCertificateKeyFile "/etc/certificates/domain.com.key.pem"
SSLCertificateChainFile "/etc/certificates/domain.com.chain.pem"
</IfModule>
ProxyPass /uploads !
ProxyRequests Off
ProxyPreserveHost On
ProxyPass / http://127.0.0.1:8080/
<Location />
ProxyPassReverse /
Order deny,allow
Allow from all
</Location>
</VirtualHost>
Cheers,
I was having the same issue and it in the end it ended up being an issue with my virtualhosts setup in apache.