I've had only a problem once when booking a redemption 3 weeks ago, website said no, called in to get fixed. Made 5 bookings, 4 cash 1 redemption in the last 3 days and all worked online first time without issue.
iOS app doesn't like me and says the password needs to be updated to be more secure but my password meets the standard required
One good thing is the rewards number is not editable anymore so my browser doesn't try to substitute my credit card number