That’s not the syntax for the function… you can’t just type the text – you need to add the function and then click on it to set the required properties from the pop-up box, and it will then fill in the correct text for you ie HIGHESTHIGH(BACKTYPE=Months, BARS=6, INCBAR=True) to get the 6 month high.
You also don’t need the LAST() or the [1] offset, so use LOWESTLOW(BACKTYPE=Months, BARS=6, INCBAR=True) for V2 and it should work.
See here for other examples of calculating ranges and levels:
https://forum.optuma.com/topic/50-all-time-high-all-time-range/