Relax, there's likely to be an easy fix.
Can the other person see any comments in the document?
If not, it's probably because they don't have enough access to the document that you're sharing. The easiest way to fix that is to change your sharing settings. Set access to 'Can comment', and then either add specific people, or set it to 'Anyone with the link'.
The other person can see other comments, but can't see mote comments
Do they have the mote extension installed? This article explains what they'll see if not: What will other people see when I create a voice mote?
They have mote installed, but still can't see my comments
Try refreshing the page. If that doesn't work, then please feel free to fill out a help request and we'll try to work out what's gone wrong.