I just got off meraveglia today, my booking showed 100. onboard credit from months ago when I booked it, I printed it out and brought it with me just incase, when I got onboard it did not show on the app, checked with guest services and they assured me that I had 100. obc, no bill was left at my cabin yesterday or today.
I did not want to go to guest services this morning so had no idea if they gave me my OBC.
I am home now, checked my credit card, I know the service charge for a 4 night was something like 112. ( I gave the cabin person a generous cash tip also, she was a doll) I know what the rest of my charges were and I can tell there is no OBC credited to my account.
Check the app once on board, if it doesn't show it under billing, I would question it because to me it's not worth fighting for100. after you get off. Have a wonderful cruise.