Easiest way I’ve found for travel package.

Step 1: convert old certificates (which takes the longest) via legacy Marriott staff. Ask when you call or you will be wasting your time with legacy SPG staff as they don’t have access to the system to cancel and order new certs.

Step 2: for SPG properties, call legacy SPG staff and make a reservation without attaching a certificate or pulling the points.

Step 3: call legacy Marriott to attach step 1’s certificate to reservation in step 2.

Done it twice like this with step 2 and 3 less than 5 minutes each.