Protocol WSS to WS does work in CloudFlare?

Hi, there!

My SSL/TLS encryption mode is Flexible

Can I use WebSocket, if in my server WebSocket protocol is running under plain WS at port 8443. At CloudFlare side is WSS and port is 8443.

Or I must use in all over side WSS protocols?

Ouch, well, in that case the best solution would be to get an SSL certficiate and setup the Full SSL (Strict) mode using Cloudflare Origin CA certificate from here:

Use websocket with WSS when using HTTPS connection.

Use WS on HTTP connection, but not on HTTPS.
If you want use WSS (websocket over TLS) use HTTPS connection.

What URL scheme and the port are you using?
Regarding your 8443 port, would be like the below example:

wss:// (HTTPS connection)

ws:// (HTTP connection)

Just to note here, ports are an example and compatible with Cloudflare (can be proxied) as listed here: