Unable to access web application deployed on my Ubuntu 16.04 machine from other devices/laptops on the home LAN

Question

I have made 2 webapps(I'm learning web development basics). One using ruby-on-rails and another using apache2.

My laptop's local IP is 192.168.122.1.

The following 2 urls are working on my machine : 1) The ROR webapp -> http://192.168.122.1:3000 2) The Apache2 App -> http://192.168.122.1

However, when I type the same URLs on another device/machine on the LAN,I get ERR_CONNECTION_REFUSED.

When I type into the terminal the following : sudo nc -v 192.168.122.1 3000 , I get the message Connection to 192.168.122.1 3000 port [tcp/*] succeeded!.

I don't think that this is a problem with rails or apache2 but is either a bug in Ubuntu OS or there's something about opening ports which I don't understand. I tried opening the necessary ports 80 & 3000 using ufw but didn't get the desired results. I tried completely disabling the firewall(not a good practice, of course) by typing sudo ufw disable. But,it had no effect. I'm still facing the same problem.

I'm using Ubuntu 16.04. I had developed a basic web app almost 4 years ago on Ubuntu 12.04 and never had to face such issues.

Iptables:

umangmathur@Acer-Aspire-V3-571:~$ sudo iptables -L
[sudo] password for umangmathur: 
Chain INPUT (policy ACCEPT)
target     prot opt source               destination         
ACCEPT     tcp  --  anywhere             anywhere             tcp dpt:3000
ACCEPT     udp  --  anywhere             anywhere             udp dpt:domain
ACCEPT     tcp  --  anywhere             anywhere             tcp dpt:domain
ACCEPT     udp  --  anywhere             anywhere             udp dpt:bootps
ACCEPT     tcp  --  anywhere             anywhere             tcp dpt:bootps
ACCEPT     tcp  --  anywhere             anywhere             tcp dpt:http

Chain FORWARD (policy ACCEPT)
target     prot opt source               destination         
ACCEPT     all  --  anywhere             192.168.122.0/24     ctstate RELATED,ESTABLISHED
ACCEPT     all  --  192.168.122.0/24     anywhere            
ACCEPT     all  --  anywhere             anywhere            
REJECT     all  --  anywhere             anywhere             reject-with icmp-port-unreachable
REJECT     all  --  anywhere             anywhere             reject-with icmp-port-unreachable

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination         
ACCEPT     udp  --  anywhere             anywhere             udp dpt:bootpc

Ifconfig:

umangmathur@Acer-Aspire-V3-571:~$ ifconfig
enp2s0f0  Link encap:Ethernet  HWaddr b8:88:e3:0b:04:c4  
          UP BROADCAST MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)
          Interrupt:16 

lo        Link encap:Local Loopback  
          inet addr:127.0.0.1  Mask:255.0.0.0
          UP LOOPBACK RUNNING  MTU:65536  Metric:1
          RX packets:15396 errors:0 dropped:0 overruns:0 frame:0
          TX packets:15396 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:1646030 (1.6 MB)  TX bytes:1646030 (1.6 MB)

virbr0    Link encap:Ethernet  HWaddr 00:00:00:00:00:00  
          inet addr:192.168.122.1  Bcast:192.168.122.255  Mask:255.255.255.0
          UP BROADCAST MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)

wlp3s0    Link encap:Ethernet  HWaddr 08:3e:8e:2a:10:81  
          inet addr:192.168.43.129  Bcast:192.168.43.255  Mask:255.255.255.0
          inet6 addr: fe80::99e9:db42:eceb:a526/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:544441 errors:0 dropped:0 overruns:0 frame:0
          TX packets:302249 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:710738799 (710.7 MB)  TX bytes:46367641 (46.3 MB)

List of listening ports(using netstat):

umangmathur@Acer-Aspire-V3-571:~$ sudo netstat -patune | grep LISTEN
[sudo] password for umangmathur: 
tcp        0      0 127.0.0.1:3306          0.0.0.0:*               LISTEN      123        23438       1110/mysqld     
tcp        0      0 0.0.0.0:139             0.0.0.0:*               LISTEN      0          31251       2361/smbd       
tcp        0      0 127.0.1.1:53            0.0.0.0:*               LISTEN      0          26992       1508/dnsmasq    
tcp        0      0 192.168.122.1:53        0.0.0.0:*               LISTEN      0          27672       1406/dnsmasq    
tcp        0      0 0.0.0.0:22              0.0.0.0:*               LISTEN      0          233420      1082/sshd       
tcp        0      0 127.0.0.1:631           0.0.0.0:*               LISTEN      0          23217       923/cupsd       
tcp        0      0 192.168.122.1:3000      0.0.0.0:*               LISTEN      1000       71774       4678/192.168.122.1:
tcp        0      0 0.0.0.0:445             0.0.0.0:*               LISTEN      0          31250       2361/smbd       
tcp6       0      0 :::139                  :::*                    LISTEN      0          31249       2361/smbd       
tcp6       0      0 :::80                   :::*                    LISTEN      0          28945       1861/apache2    
tcp6       0      0 :::22                   :::*                    LISTEN      0          233422      1082/sshd       
tcp6       0      0 ::1:631                 :::*                    LISTEN      0          23216       923/cupsd       
tcp6       0      0 :::445                  :::*                    LISTEN      0          31248       2361/smbd