Duping in Terraria is really easy

All you need is a chest (or chests depending on how much stuff you got)

Step 1: Backup your character multiple times, preferably to local as I haven’t tested cloud saving.

Step 2: Use those backups and deposit whatever you want to dupe into the chest

Step 3: Go back to your original character, and collect the stuff your copies deposited.

Step 4: Repeat as much as necessary.

No is Nø