This is the first time I've tried to use the DEBUGSTR() (and associated functions) utility provided in such board. However, it seems that the PIO0_18 and PIO0_19 pins ARE NOT pinned out to any of the several board's connectors.
What am I missing?
I found the answer. Such pins aren't pinned out; instead, they are connected directly to the LPC4322 chip (the one that serves for debugging) so we can use the USB port for the UART. It means we don't need either the pins pinned out nor a TTL-USB adapter, awesome!
I documented my discovery in my blog in case you're interested in the topic.
Thank you!!!