Carnival eGift cards - apply now or wait? Cruise not yet paid off, third party TA

I have a total of (4) Carnival eGift cards.

$100 - from AARP

$300 - from the 15% eBay digital gifts.

My cruise is not yet paid off (final balance not due until this November), and cruise was booked via third party TA, not Carnival Directly.

Now, as I understand it, it seems that most folks say to apply the eGift cards ASAP so that people can't "guess" the number and use your balance.

My understanding is also that if I apply the $400 in gift cards, it will go towards reducing the final payment amount, yes?

My issue/question, is if I do that:

a) will the third party TA know or just go ahead and charge my card the original balance owed?

b) If they do charge the original balance, will this cause problems with Carnival or will they simply apply the extra as "OBC" or something?

I just don't want my cruise getting cancelled due to some oddity with the system.

My original intent with the GC, BTW, was to use as OBC for adult beverages and things, but I suppose it all works out the same, regardless.

If you want to apply the gift cards towards the cruise, you have to call your TA to do that, you can't call Carnival directly to make a payment if you have a TA. You call the TA, give the TA the gift card number, and the TA calls Carnival to apply the gift card towards your balance due on the cruise.

Some TAs apparently will not do this, but many do. I don't know why. You'll have to call your TA and ask if they will.

I just purchased 5 $100 ecards from AARP. I sent 3 of the Card #'s and pins to my TA and asked her to apply them November cruise balance- she did and sent me a new statement from Carnival reflective of my new "Balance due" .

I kept 2 gift cards for my July cruise (I will go to the service desk and ask them to apply them to my on board account to pay for my gratuities and other "stuff").

Thanks for the info!

I hated it once I booked a Disney cruise and was buying $50 giftcards from target to get the 5% discount on them and she ended up having to apply like $6000 worth of giftcards I tried to be nice and not give her to many at once - but you know i figure it this way they are getting paid to do this so if my TA is not willing to apply my giftcards I am gonna give them the boot