Came across this thread trying to resolve the same issue, sharing my experience for others in future months/years.

Website refused to load domestic flights within Brazil. I tried mobile and desktop, incognito windows, multiple different country sites, downloaded the LATAM app, cleared cache, used mobile data, nothing worked. This is a LATAM issue, not a Brazil issue: online bookings with Azul and GOL went through with no major issues.

I called the Canada/USA customer service line to book four flights and, to their credit, this is clearly something they're used to handling. Got an actual person immediately after bypassing the horrible AI bot. Gave the dates and flight numbers I wanted, prices over the phone matched the USD figures from Google Flights. Some flights were not available however: there was a creative two-stop flight from REC to SSA that priced out quite cheap in premium econ on GF and listed a price direct from LATAM, call centre agent couldn't book it or even see it as an option. Ah well. No fee for booking over the phone, agent proactively waived it since they know this is an ongoing issue.

One other "feature" of LATAM's IT set-up: my Canadian credit card kept getting refused when entered into their phone system. The automated system prompted me to "press star" after entering my card number...when I did this (or pressed pound instead) the transaction failed, when I just entered my card number and waited for 5-10 seconds it went through.

Agent confirmed the USA/Canada line can only sell flights in USD.