Typically you need to hold the standby button on the remote for a couple of seconds or so. The Pro Box will turn off immediately & the TV shortly after. Assuming that the remote is actually controlling the TV volume & not that of the Pro Box, then the longer button press should work.
Although be aware that many lower end TVs aren't necessarily made by the manufacturer whose badge is on it. So that causes a mismatch between the IR codes that the Pro Box chooses based on the manufacturer & those actually in use by the TV. There's no way round that other than buying one of the older model IR only remotes. Even then the required codes may need some guesswork & still might not be available.
