Hi Lucy 
It is disheartening when you launch something and it didn’t have the uptake you anticipated. I have experienced this myself in the past before. I’ve had a gander at the link in your bio (https://www.protoexpress.com). Some observations…
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Had you not mentioned SierraConnect in your topic above I would have no idea where to look on the website. From my experience, many sites have a link to their forum in the header or footer clearly marked ‘Community’. Because its difficult to find people visiting the site don’t know it exists and are less likely to join.
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I can see you’ve utilised tags which is good. However, there is a large amount of categories. This can make new users a bit scared to post new content Imagine facing a wall with 15 doors. Which door do you open? To then be faced by more doors (subcategories) This blog article makes some interesting points about why more categories isn’t always better.
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Not sure if you have any control over the website but I’ve noticed that the sites KB (knowledge base) and support / contact us pages are separate. What I mean is that companies normally provide KBs and product support on the forum. Here is an example of what I think it should look like Contact the Discourse team | Discourse - Civilized Discussion. Point users towards the community. Not sure if you are self hosting or a hosted customer but I’d look at getting the Docs plugin to help organise your KB.
I’ve found these blog articles helpful to look at in the past and I have found them helpful on many occasions. Not sure if you’ve already seen them
Hope this post didn’t sound negative that’s not my intention 
Just offering my perspective on it. I may be wrong about stuff I’ve posted.