The issue is with your DNS configuration for rubaru.app. Currently, you have “hardcoded” three IP addresses. However, one of the three IP addresses (147.75.108.42) is not a boundary node anymore. Hence, when users get directed to that address, they get the internal server error.
Ideally, you setup a CNAME / ALIAS / ANAME record for your domain instead of hardcoding a few IPs. If you DNS provider doesn’t support one of the three record types for apex domains, you should think about switching to a different provider (e.g., Cloudflare). You can find instructions here.
If you have any questions about how to go about it, just let me know!