You should be able to use AARP egift cards to pay for your cruise with PCL/TA/CVP. over the phone.
However, when you use them precruise, to put OBC onto your account, it is more difficult. I called 3 times and tried to add them for OBC to my cruise, so I could book excursions. It is a difficult transaction for the agents, as 3 different agents had a hard time adding them. They said it was added, didn’t show up, called back and agent tried again, the 3rd time, agent double added it. The last time I got a customer solutions agent and she reinstated it on the account, as it had totally been removed. Make sure you see the gift card added to your account, IF you do it ahead of the cruise.
Then, I decided I would only use ahead of time towards payment and if I had any left, I would ONLY take them to the Elite/Suites GS line to be added once OB.
They usually have more experience with the cards. I will then purchase my excursion once OB.