502 Gateway Error

Hello. I already try that solution. In fact, according to Cloudflare there is a 502 error but when I redirect my domain directly to host or pausing on Cloudflare website works as perfectly. I believe problem is in the Cloudflare. I contacted with my hosting company many times and they confirmed me there is no problem with server.

grandmount.org - Cloudflare OFF
bkvideography.club - Cloudflare ON

Both websites DNS redirected to Cloudflare.