If you search for a domestic Peru airfare on Google flights, it always brings up 2 fares for the flight: a lower one with the comment “book on LATAM’s Peru site,” and a higher fare that says “book on LATAM’s US site.” (The fare difference starts at about $20 and can be as much as 50%, this is for the same seats)
The issue with using the Peruvian site is that it is all in Spanish. Since only Americans seem to be targeted for the higher fare, the work around is to use another English speaking country to access the lower fares but still navigate the ticket purchasing process in English. The NZ site is one easy way to do this, https://www.latamairlines.com/nz/en
which I just used 3 times to buy the lower LATAM airfares. The NZ site also conveniently defaults to US $.
At first entry you will be required to select either “remain on the New Zealand site” or “switch to the USA site” so chose NZ, or paradoxically sometimes the choice is is Spanish asking whether you want to switch to the USA site or remain on the Peruvian site, in that case choose Peru but the process continues in English.
[Sorry, I don’t know where Canada falls in this, or the UK.]