user95071: I have BTCPay server and would like to use external c-lightning node which i have funded and prefer more over BTCPay server local docker container (DC). 
In store configuration i see that there is option to connect to c-lightning over tcp or unix socket (this one is used when i connect internal node because c-lightning DC socket is linked to BTCPay directly).

How can i connect over TCP? As i uderstand this is not public nodes port (9735) which is used to communicate between nodes but some API port? How can i enable it on c-lightning? Is data sent plain and i should secure communication (lan, fw, vpn etc.)?

user21478: Port 9735 is the lightning port. What BTCPay wants is the API.
C-Lightning does not support TCP natively, but one can use socat as I did in the docker entrypoint to bridge unix to TCP.

95071: <p>I have BTCPay server and would like to use external c-lightning node which i have funded and prefer more over BTCPay server local docker container (DC). </p>

<p>In store configuration i see that there is option to connect to c-lightning over tcp or unix socket (this one is used when i connect internal node because c-lightning DC socket is linked to BTCPay directly).</p>

<p><a href="https://i.stack.imgur.com/IGJXM.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/IGJXM.png" alt="screenshot of store LN payment configuration menu"></a></p>

<p>How can i connect over TCP? As i uderstand this is not public nodes port (9735) which is used to communicate between nodes but some API port? How can i enable it on c-lightning? Is data sent plain and i should secure communication (lan, fw, vpn etc.)?</p>
 21478: <p>Port 9735 is the lightning port. What BTCPay wants is the API.
C-Lightning does not support TCP natively, but one can use <code>socat</code> as I did in the <a href="https://github.com/btcpayserver/lightning/blob/master/tools/docker-entrypoint.sh#L15" rel="nofollow noreferrer">docker entrypoint</a> to bridge unix to TCP.</p>
