I tried using that code and it didn't work. Emailed Amazon about it and they replied:
Hello,
I understand that you're unable to use the coupon code "FAMILYPHOTOBOOK50" on Amazon Prints. Please accept my apologies for the inconvenience caused due to this situation.
I've checked our records, however, I see that the coupon code which you're trying to use is invalid.
I'd request you to contact the website on which you've found the coupon, as they may be able to provide a new coupon code.
If in case, you have received the code from us, then please send a screenshot of the e-mail including the code by replying to this e-mail.
Your patience and understanding is much appreciated in this regard.
However, if you still have any questions, we'll be better able to answer them over the phone. We can be reached by phone 24 hours a day, seven days a week using the following link:
https://www.amazon.com/gp/help/contact-us/cloud-drive.htmlWe look forward to hearing from you soon.
We'd appreciate your feedback. Please use the links below to tell us about your experience today.
Best regards,
Shyam