Monster Vision TV IR REMOTE.

You can't expect Roku to know the codes for every TV manufacturer there is. There are so many odd brands that are built under spec for someone else.

A quick web search found that Technosonic is the core for many "off" brands. I don't know if they are listed in the Roku remote list, but take a look and see if one of their codes work. Based on my search, Roku isn't the only brand that is missing brands like this. The Fire TV has the same questions for their remotes.