Klook is currently offering US$5 off any activity with code "VIEWREVIEWED5" until 2nd July 2022.
Found in a post - https://www.facebook.com/100594575972135/posts/pfbid0HcXLK5F…
Not sure whether there is a minimum spend.
Edit: It seems to only work if you click through the link in the Facebook post, otherwise a pop up will come up saying "To use this promo code, please go back to the page/email you found it and select the partner's link".
Mod note: The Facebook post contains an affiliate partner's link required to activate the coupon code.
Nice. Thanks, OP, booked a near-free airport pickup service.