To order an additional copy of a previously ordered Monthbook, log into your account on Chatbooks.com and select the subscription you want to reorder from. On the next screen, click Monthbook that has the "Buy Again" prompt.
If you tap the Monthbook, you'll see a "Send to Print" option in the upper right-hand corner. Click "Send to Print."
Once clicked, confirm that the details are correct, then click "Send to Print." Your copy has been ordered!
Learn how to do this on the Chatbooks app here.