I find its just a problem of lack of instructions on steemit. If you are a youtube member moving over to dtube, it doesn't say when you register where you have to go in your wallet to get all the specific passwords you need and how you activate them. Some simple prompters would be useful.
Steemit.chat has a separate account system. It's not related to Steemit.com except that it is linked from this website (it's not run by Steemit Inc either).
DTube only allows you to use your posting key, not your master password. This is to help prevent you from leaking your master password by accident.
How to find your posting key
I don't know what Grammarly is, never heard of it.