Conference disconnects after 30 seconds when second participant joins

I have recently set up my own self-hosted server using this guide.
Now the problem is When I start meeting through the browser it’s working well but when I start a conference in Mobile SDK it automatically terminates after few seconds when the second participant joins the call. My server URL is the following

SSL certificate seems fine as I have generated as per the documentation from let’s encrypt. Please let me know what could be the issue? Just to clarify that when I use this host then it works well. The problem is only on my server-side which is working for the browser but not for the mobile SDKs. Thanks in advance.