You can always verify how much you’re paying for a subscription credit by reviewing your subscription Settings.
For Monthbook or Monthly Mini books in the Chatbooks app:
Open the Chatbooks app
Tap into your Monthbook Subscription
Tap into Manage Subscription
At the bottom of the screen, under Billing cadence, you'll see your current subscription price.
This amount reflects what you’ll be charged for your upcoming book credit. You can then use this credit to send a photo book to print.