It could be an error. I tried booking a C+P+DSU without enough points and the agent booked me something, but it actually ended up being revenue rate plush points suite upgrade. I reached out to the rep here who told me
"Points + cash rates require the points value to be in the account, however, standard points options and suite upgrades do not"
So, double check because I was unable to do so (but the phone rep booked me something else mistakenly).
Fdw