Keep at it, I have the same issue at times. Often I think I am harmonizing the octave in my head already. Try singing it? Route IV is using root chords and the bass notes are a good indicator.

It's very common and even expected, the advice I can suggest is to use an instrument along with the game, and dedicate time for playing the game (exercising and sweating) daily, keep at it as Amilwhat said. Over time might take a few months you will be able to forego the instrument

4ths and 5ths can be confusing due to a descending 5th is the same an ascending 4th. I find it easy to visualise playing and hearing these sounds on my instrument as they're common movements.

Best advice i got: a P4 is Here Comes The Bride. So if u can sing that over the interval and u hear both notes in it then thats the one ;)

Route VI uses only root position so far (I'm on level 71). As Amilwhat ? has said, listen for the lowest (root) note of the chord. They do jump octaves, depending on the key, but they are all root position.

Listen for the bass notes. You can tell if they're ascending or descending. That usually allows you to eliminate a couple of the choices and can help you find the overall shape of the progression. If you can pair that with the interval recognition from Departurer and Lander, it gets pretty easy to find the progressions.

In the early levels, if the progression starts on I and goes down, it's usually I-V. If it starts on I and goes up, it's usually I-IV. This gets less consistent in the later levels, but by then you probably will have developed a better ear for what a IV or a V sounds like in relation to the I.

@Adam Ritchie what do u mean by descending 5th is the same as ascending 4th?

@Aruna Abrams omg thank u this helped me a lot!

@David Loving ok ty i'll try that!

Aruna's suggestion is very valid. Finding songs with initial melodic intervals matching the possible intervals in an octave, ascending and descending, is a big help. All the games in ToneGym are beneficial when taken together ... each informs the others.

4th = la marseillaise (french hymn)
5th= chariots of fire (vangelis)

This had worked great for me 😁

@Lauren LovesCats If you for example take the notes C and G. If you decend from C to G, you have a 5th but if you ascend from G to C, you have a 4th.

It took me months to pass just a few levels on Route VI. It was my worse game but now I like it. The above info is gold, thanks everyone. KEEP PUSHING @Lauren LovesCats :D