Post request in 3rd party endpoint Failed time out

I deploy my laravel app to digital ocean droplet. everything work fine. when I send post request from my server to my 3rd party end point 196.188.120.3:38443/…, respond me with timeout error. here is what did so far

• test different 3rd party end point with port 8080 and it work fine(working),
• test in postman 96.188.120.3:38443/… it works fine (client server working),
• test in 96.188.120.3:38443/… local environment it is working fine (working),

My suspension on this problem is

• my Firwall outbouding error, sudo ufw allow out on eth0 to any port 38443 i add this rule(noting change),
• curl -kv 96.188.120.3:38443, stil time out,
• review my nginx (but i guess its for inbounding request),
• i also setup cloudflare (but i guess its responsible for inbounding, i proxy orange, but i guess its not change my outbounding ip address),
• they(3rd party end point owners) told me send them ip address and port to white list (I send them my droplet ip address and port (443) because i my site is https from cloudflare), u think its wrong ?
• everthing i try is failed. I run thin in my droplet terminal iptables -A INPUT -p tcp --dport 38443 -m conntrack --ctstate NEW,ESTABLISHED -j ACCEPT but still failed

any idea please i have this issue for week, I am stressed thanks