Error messages explained
Oops... Couldn't find admin installation
OneClick seems to have an issue with admin user's credentials that are needed for the application to operate.
Please ask your Pipedrive admin, who has OneClick installed, to re-authorize the application through this link to refresh the admin's credentials.
Missing admin user installation
It seems that your organization has no OneClick installation from a Pipedrive admin user present. At least one Pipedrive Global admin has to have a OneClick installed in order for the application to be able to operate.
If you are an admin user yourself and actually have OneClick installed, please re-authorize through this link in order to be able to refresh your credentials.