Can't connect to server via android and ios


I created my own chat server in the chat to communicate on it.
It was used only in the university network on port 3000, after which port 3000 was ported to work outside the university network. It went well!
Works on any network, but only through computers.
When connecting to a server in an Android or iOS app, a “connection closed” error occurs.
After reading the forums, I realized that in order to work in the application, a letsencrypt certificate is required, which I issue through certbot.
So, the certificate does not want to issue, an error occurred: Failed to make a call for the domain

Timeout during connection (probably a firewall issue)

To fix these errors, make sure your domain name is
entered correctly and the DNS A/AAAA records for that domain
contain the correct IP address. Also, check that
your computer has a publicly routable IP address and what doesn’t
firewalls are blocking server communication with
customer. If you are using the webroot plugin you should also check
that you are serving files at the root path you specified.

The problem with the firewall is that it is completely disabled.

I also studied letsencrypt and certbot, I realized that they need port 80
but I can’t use it, it’s already taken at the university!
I do not know what to do. I need your help!


Application engine version


Version Node



4.2.17 / wiredTiger (oplog on)

proxy Nginx

Hi! indeed, the mobile will only connect to a secured SSL domain.

I am not sure Let’s Encrypt allow other ports then 80 and 443, maybe with dns challenge. AFAIK it doesn’t.

You can get a working certificate (not from Let’s Encrypt) and install it according to here:

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But one problem, the link you posted shows how to configure nginx with an already existing certificate (as I understand it), but I need to get it.
Through caddy, as indicated there, it will not work either, since port 443 is needed, which is busy.

Yes. that seems to be a limitation on Let’s Encrypt side.

Once thing you may do is to ask for a wildcard certificate from let’s encrypt or other certification issuer, and then configure it manually, according to docs.

Be careful with your own wildcard certifcate and Caddy usage.
Try my owns … and fail to connect with android (work with IOS … arf … appeule … beurk !) because the entire certifacte chain can’t be configured in caddy (only key and pem, not he crt needed).
It’s work only if we had the crt certificate on our mobile device … not friendly with external mobile to communicate.

So, we use caddy and the auto signed letsencrypt’s certicate

Thanks for the help!
I will keep trying!