A 0% deposit works like "try before you buy". The buyer's card is saved at checkout, but nothing is charged. The full amount is charged when you fulfil the order.
It's useful when you can't promise stock yet, for example for allocations or group orders. If you never fulfil the order, the buyer is never charged.
Where to find it
Depositly → Purchase options → your offer → Offer terms
How to set it up
Open your offer and go to Offer terms.
Under Balance due date, choose On fulfillment.
Set the deposit to 0 (percentage or fixed amount).
Click Save.
Good to know
A 0% deposit only works with On fulfillment. On any other timing, a 0 charge would collect nothing.
It only works in automatic mode, because a card has to be saved.
It works with one balance, not installments.
You can see the order and saved payment method in Shopify admin → Orders.