Two problems:

1. You can only stopover (>24 hours) in one of your two entries to NA. The other entry must be a transit without stopover between another continent and South America.

2. This is a *ONE5 trip, not *ONE4. Even though you do not stopover in Asia the LHR-MEL segment assumes an Asia stop. ((You actually do land at SIN but you would be hit with the extra continent charge even if you didn't.)