Is anyone using a Smartthings Hub with HA and not using the integration? Maybe a 3rd party service like IFTTT?
I use a Synology and it is using port 443 on the internet for another service already. It seems every api service like Smartthings “requires” 443 “just because” and I’m screwed with anything I try to do. sigh
Well, after an hour or so I figured out how to use Synology’s Reverse Proxy service to get 443 working along with the other service. I just assigned HA it’s own DNS name eg https://homeassistant.example.com
I can get to that internally and externally now, which is cool. I still can’t get Smart Things to connect. I’ve followed the instructions and when I get to the last set and click my “Home Assistant” app in SmartThings all it says is “Something went wrong.”
My cert checks out. In troubleshooting I used the curl command test and got the expected result. My base_url seems to be okay. It might be something with Synology’s Reverse Proxy, but I don’t know where to dig into that…
I’m having a similar problem - HA is set up (running in a Linux VM), SSL set up courtesy of certbot, and seemingly working fine to the outside world. Generated a token on the smartthings site, add the integration via the HA web ui. It shows up in the classic android app, but when I click on it to finish the integration, I just get a red bar that says “Something went wrong” with no other info. 
Sorry your luck is the same as mine. Fortunately, I was able to return mine. I ended up with a Vera Plus refurb that was easy to use with HA. It’s got some of it’s own quirks, but it works.
I would be interested why you are using a vera plus or smartthings for that matter. Is it for the radios? Buy a USB zwave and a zigbee stick.
For me, it’s personal preference. My Synology runs a lot of services, mostly in Docker containers including HA. I didn’t want to mess with getting USB sticks working for a couple of reasons. 1) I don’t want to attach any hardware to my Synology. It’s a nice 8 bay unit and I want it “stand alone.” 2) every now and again there are rumblings on the Synology forum about USB support. I didn’t want to take the chance that some update would break things or that some day I’d upgrade the unit and they will have moved away from USB all together.
Having the Vera - which I got a refurb unit for $50 US - was a good and quick way into Z-Wave and Zigbee with a controller HA supports and saving a fair amount of configuration time if, say, I built my own with a Pi or something. Plus, it’s stand-alone. If I ever change the Synology or move away from HA (I doubt that!) I’d still have at least all of those devices configured with it for the “next thing.”
The Synology is a Linux box. It has support for USB(that is part of the Linux kernel). They won’t be taking that support away anytime soon as it would be way too much work. I think there are plenty of examples on here of users using USB sticks with Synology NAS. Either way I am just trying to be helpful the USB solution is one you can use and had a little less kluge.