Yes, quite a few people have also tried booking their complimentary dinners, two per guest, and have been asked for their credit card. I had no problem booking them with no credit card prompt to pay. I believe that if you pay, upon boarding a trip to GS will have the amount charged applied as refundable OBC.
A few of our members contacted Princess and received this response. However, I don’t recall anyone coming back to report if they were successful. Hopefully, someone will chime in who has experienced this.