Load balancer see site Down even with Host set


I’ve set up a load balancer with 2 server monitored.

They are monitored the same way on HTTPS on /login page with the same Host.
This is working on Postman since I got the right 200 response and page content when I go to https://theipaddress with the right host header.
But on Cloudflare it keeps showing the second server as down without any further explanation than code mismatch.

Thank you,