I'd try a private/incognito window and other browsers just in case some extension is blocking CC authorisation pop-up. Only had a problem with my first Malindo booking and it's been fine (with a Cdn CC) since. Not that I've made a booking on OD in 5 years (but have with Firefly, Malaysia, Air Asia (AK) x 2, and Vietnam Airlines x 2 the past few months.