As Xalius mentioned, voltage matters! Standard RS232 serial could be as much as -15 to +15 (30v full swing) as opposed to the 3.3v/TTL that is required by the A64/RK3399 used in the Pinebook/Pinebook Pro. Meaning depending on how true that cable is to the spec, at minimum it could fry the RX/TX GPIO pins, and possibly fry the CPU completely.
Information on the pinout, baud rate, etc is here on the wiki.
Information on the pinout, baud rate, etc is here on the wiki.