Originally Posted by ftrichard

1) Confirm with the Design Hotel that they participate in Marriott Bonvoy and that your pre-paid rate is eligible. Assuming the answer to both is "yes" then supply them with your Bonvoy number now, confirm it when you check in, and confirm with them when you check out that they will post the stay. AFAIK, Design Hotels manually enter your stay on a portal after you've checked out. That is to say, the posting is not automatic by Marriott's reservation system because they don't use it. I've never had a problem with points and nights posting from Design Hotels that participate in Bonvoy but not all of them do and you're best to confirm this up front to, as they say, avoid disappointment.

2) The critical moment will come when the stay posts but you have at least three months to complete the challenge so I would ensure that you are unambiguously registered before you approach the check in day for your stay. It doesn't matter when you make the reservation. Indeed, being a Design Hotel that you've booked directly, Bonvoy will not know anything about your reservation until they post the stay manually after you've checked out. I regularly stay at a Design Hotel that I book directly by email and the reservation never appears in the Bonvoy app but the stay posts the day after I check out.