Tagging options are only available for Facebook, LinkedIn and Twitter at this moment. We'll see the both cases below.
Facebook. You can tag a page by typing "@pagename" (exactly as it is on Facebook), our system will search through all the pages and find yours. Unfortunately, due to Facebook API restrictions we're unable to tag Facebook Profiles.
Find the username of the page by going to their Facebook Page. It's displayed in the name and URL of the page.
Sometimes, we might have too many requests being sent to Facebook (like tagging, scheduling, publishing, connecting etc.) which might not display the tagging of the post. If this happens, please try again in a few minutes, it usually works.
We're currently working hard on becoming Facebook & Instagram Marketing Partners which would allow us to make sure it won't happen in the future.
Twitter. It's exactly the same workflow for Twitter, type @[account name] and it will appear in a list below, here's a quick GIF to show you how it works.
LinkedIn. Same as above, just type the exact handle of your LinkedIn Company Page and then type this in the composer, here's how.