The Vaults Spending Reserve feature allows you to control whether funds will be automatically moved from your Vaults to cover any purchases.
When you enable Spending Reserve, funds will automatically be transferred from your Vaults to cover a negative account balance as long as there are sufficient Vault funds.
Please note funds will not be swept from vaults when a SoFi Money debit card purchase is in a pre-authorized state (pending, hold placed on the account, but no settlement/posted transaction yet).