I don’t know why it would be an empty response, though. Cloudflare usually includes a 4xx or 5xx response code if it’s not a successful 200 connection.
Have you checked your server logs, or even the Cloudflare Firewall Event Log?
At this point, I suggest you create a ticket here and then post the # in this thread.
To contact Cloudflare Customer Support, login & go to https://dash.cloudflare.com/?account=support and select get more help. If you receive an automatic response that does not help you, please reply and indicate you need more help.
Hello, I solved my problem. Issue was in TLS version. Unitpay.money cant work via 1.3 TLS version but in Firewall rules thats function was enabled. When i changed TLS version to 1.2 Unitpay handler returned me “format error response” that means my payment-handler gives wrong JSON answer to unitpay query(but it isnt, because when i turn off Cloudflare proxy all works fine).
A step earlier, I deleted the rules in the IP lists and transferred the rules with IP addresses to the Firewall with a bypass, as you recommended, but it did not help. And when I saw that the answer from unitpay.money was no longer an empty answer, I went to watch the Cloudlfare`s firewall events. And there I found the following log
As you can see Cloudflare blocked Unitpay query to my site according Bot Fight mode rule. So the last step was revoke deleting rules in IP Address list and set “Allow” again. And its works!