https://www.grab.com/my/blog/suregrab/

Just simply enter the eligible areas(i.e. Bangsar, Sunway) as the pick up point, then choose some ridiculously far/remote areas(i.e. Gerik, Gua Musang) for drop-off, get rejected twice then you will get free RM8 promo code from grab within 72 hours.

It works, just use the same pick-up point. The bangsar/TTDI example on the FAQ page means your first booking attempt in Bangsar, 2nd booking attempt in TTDI, so not eligible.