As well as @cpu’s advice it could be worth thinking about (or if you have a networking team at the Company asking them) whether the MiCollab server will be able to connect to Let’s Encrypt’s services out on the Internet, and then (though it hasn’t got that far by the looks of things) whether Let’s Encrypt’s servers will be able to connect back to your MiCollab server.
I haven’t used MiCollab but from the blurb it sounds like a system most people would have facing the outside world, in which case this shouldn’t be a problem, but of course your Company might intend to use it in a different way, or the fact that it’s new and you’re still setting it up could mean it isn’t yet exposed to the public Internet.