Cloudflare can only proxy traffic going over the HTTP/HTTPS ports listed below. If your traffic is on a different port, you should create a subdomain for that record and then add it as a record in your Cloudflare DNS zone file as something we don't proxy (gray cloud = no Cloudflare proxy or caching on a record).
For requests made via HTTP:
For requests made via HTTPS:
On the pro plan and above, traffic on ports other than 80 and 443 can be blocked using WAF rule id 100015: "Block requests to all ports except 80 and 443".
Ports 80 and 443 are the only ports for HTTP/HTTPS within China for zones that have the China Network enabled.
Ports 80 and 443 are the only ports for Cloudflare Apps to be able to proxy on.
Ports 80 and 443 are the only ports where Cloudflare Caching is available.