Facing Error :The request to the authentication proxy has failed with an error

Thanks for getting in touch @larsmeyer. Based on the error you’re encountering, and the checks I performed on your site, I suspect your site may have been successfully connect with Site Kit previously, although with some different site records. To determine more, and ensure you can complete setup, please share the following:

1. Your Site Health information. You can use this form to share privately if preferred.  
2. As it looks like you’re using a custom wp-login page, if you deactivate Elementor or any other plugin that allows you to customize your wp-admin path, are you able to then complete setup successfully?
3. Do your recall setting up Site Kit on this site previously? This can include with a variation of the domain name (such as without the www prefix), with a different wp-admin path, or with WordPress in in it’s their directory.

Let me know if you have any questions with the above. Thank you.

I’m just following up with you to check whether the error remains? If so please share the information requested above and we can investigate further.

As we didn’t receive a response I’ll mark this as resolved. Feel free to open a new support topic if you continue to encounter issues, or reopen this topic and we’d be happy to assist.