Since 12:35 UTC, Integrations → Connect Plesk connects a Plesk Obsidian server the way cPanel/WHM with root already works. You paste a few commands as root; they install a short script, shown in full, that reads Plesk's own list of domains with one plesk db query every ten minutes and sends it to us. A Plesk API key would carry the administrator's full rights, so we don't ask for one.
Each domain with hosting (main, additional and subdomains) gets an HTTPS monitor, grouped by server. Forwarding-only domains, aliases and wildcards are skipped. A suspended or disabled subscription pauses its sites, and a domain that goes away is paused at once and removed after 24 hours. Resellers can turn on one customer account per Plesk subscription, named after its main domain.
The integration has its own page, Plesk uptime monitoring, and the steps are in the docs.