At the time, the "company" was just my co-founder and me. We were essentially going to fail/give up by taking on consulting work. The decision to integrate with Slack was a bit of a bet-the-company move. We were building an internal wiki to compete with Confluence. Our early beta users told us they'd use our MVP, and when we gave it to them, no one actually did. When we asked, they just said, "We just keep forgetting. Still interested." We then asked about hooking up our wiki to Slack so you could search from Slack and get notifications for new content, and they wanted that desperately. Some teams even pre-paid us to build it for them. So we scrapped our whole MVP and three months of work, and rebuilt the entire product on top the Slack platform in two weeks over the holidays.
When I say, "on top of Slack", I mean we literally used Slack's APIs as our backend and just rebuilt a "wiki" front end serving up Slack files from the APIs. We even deep linked to their Post as the editor in our wiki. The goal was to validate demand so we did it as leanly as possible. Once we launched, we got about 200 sign ups in 48 hours. From there, we built a real product, which is now tettra.com.
I wrote an article about the pros and cons of building on another company's platform about a year after that which goes into more details if you're interested: https://thinkgrowth.org/building-on-slack-saved-our-startup-...