My Chat with Amazon CS:

Me: Hi, I just did a promotion where if I posted an answer to facebook and shared it, I qualified for a $5 Amazon credit. The credit however is not being applied to my account.

Veena:promo was expired, hence as an exception aplied $5 promo

Me:I'm sorry?

Veena:Please allow me a minute or two while I research this for you.

Me:Thank you.
I did the promotion while it was still alive
It said $5 has been credited, but it doesn't show up when I try to checkout.

Veena:I'll apply $5 promotion redit to account.

Me:Thank you.

Veena:Promotional certificate has been issued.
Is there anything else I can do for you today?

Me:So when I go to checkout next, it will show up?

Veena:Yes.

And BOOM... It works.