I found this thread useful as was just pulling my hair out after finally having time to listen to some MQA tracks only to find none of my Tidal tracks were accessible from the MC200.
After a quick bit of internet searching, I found that Tidal have deprecated the username and password access and moved to a more secure process. Hence why a firmware update (confirmed in this thread) is needed.
Time to get the Dragonfly and Oppo headphones out...

At least it looks like Meridian are trying to support us which is very appreciated.

Various from vintage to SE